Polypropylene film, metal layer-integrated polypropylene film, film capacitor and film roll

ABSTRACT

A polypropylene film which is capable of suppressing blocking in a rolled polypropylene film. The polypropylene film has a first surface and a second surface, contains a polypropylene resin as a main component, and is configured such that: the Svk value (SvkA) of the first surface is 0.005 μm or more and 0.030 μm or less; the Spk value (SpkA) of the first surface is more than 0.035 μm and 0.080 μm or less; the Svk value (SvkB) of the second surface is 0.005 μm or more and 0.030 μm or less; and the Spk value (SpkB) of the second surface is 0.015 μm or more and 0.035 μm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/930,839, filed Sep. 9, 2022, which is a continuation of U.S. patentapplication Ser. No. 16/767,092, filed May 26, 2020, which is the U.S.National Phase under 35 U.S.C. § 371 of International ApplicationPCT/JP2018/047983, filed Dec. 26, 2018, designating the U.S., andpublished in Japanese as WO 2019/131815 on Jul. 4, 2019 which claimspriority to Japanese Patent Application Nos. 2017-249788 and2017-249799, both filed Dec. 26, 2017; Japanese Patent application No.2017-252094, filed Dec. 27, 2017; Japanese Patent Application Nos.2018-240389, 2018-240392 and 2018-240394, all filed Dec. 22, 2018; andJapanese Patent Application Nos. 2018-243115, 2018-243118, and2018-243125, all filed Dec. 26, 2018, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention (first present invention, second presentinvention, and third present invention) relates to a polypropylene film,a metal layer-integrated polypropylene film, a film capacitor, and afilm roll.

BACKGROUND ART

Polypropylene films have excellent electric characteristics such as highdielectric strength and low dielectric loss characteristics and alsohave high moisture resistance. Therefore, polypropylene films are widelyused in electronic devices and electrical machinery and apparatus.Specifically, polypropylene films, for example, are utilized as filmsused in high voltage capacitors, various switched mode power supplies,capacitors for filter (for example, convertor and inverter), smoothingcapacitors, and the like.

In recent years, miniaturization and increase in capacity of capacitorshave been further demanded. In order to improve the capacitance withoutchanging the volume of capacitor, it is preferred to decrease thethickness of film as a dielectric. Therefore, there is a demand forthinner films.

However, thin polypropylene films have a problem that wrinkling andwinding shift are likely to occur in the element winding processing atthe time of fabrication of a capacitor. Hence, there is a case in whichfine irregularities are formed on the surface of polypropylene film toroughen the surface mainly for the purpose of improving the slipperinessat the time of element winding processing and facilitating the elementwinding processing.

Patent Document 1 discloses a biaxially-oriented polypropylene film forcapacitor which has a thickness of 1 to 3 μm and in which the number ofprotrusions (Pa) present on the surface A per 0.1 mm², the number ofprotrusions (Pb) present on the surface B per 0.1 mm², 10-point averageroughness (SRzA) of surface A, and 10-point average roughness (SRzB) ofsurface B satisfy predetermined relation when one surface of the film isdenoted as surface A and the other surface is denoted as surface B (seeclaim 1).

Patent Document 1 describes that the biaxially-oriented polypropylenefilm for capacitor has excellent processing suitability although thefilm is a thin film and exerts high dielectric strength even under awide range of ambient temperature conditions from a low temperature(−40° C.) to a high temperature (150° C.) as an effect of thebiaxially-oriented polypropylene film for capacitor having theabove-mentioned configuration (see paragraph[0023]). With regard to theprocessing suitability, it is specifically described that the occurrencerates of wrinkling and shift are low when the element winding processingis performed (see paragraphs[0122] and[0123]).

Moreover, Patent Document 2 discloses a biaxially-oriented polypropylenefilm in which both surfaces of the film are provided with protrusions,the heights (PhZ) of most protrusions among the protrusions on eachsurface are 100 nm or more and less than 400 nm on both surfaces and thenumber of protrusions (Pc) per 0.1 mm² on each surface is 150 or moreand less than 500 on both surfaces (see claim 1).

Patent Document 2 describes that the biaxially-oriented polypropylenefilm has high dielectric strength, suitable element processability, andexcellent squealing characteristics particularly in the applications ofAC voltage capacitors since the film has a surface with a large numberof low-height protrusions on both surfaces of the film as an effect ofthe biaxially-oriented polypropylene film having the above-mentionedconfiguration (see paragraph[0025]). With regard to the elementprocessability, it is specifically described that the occurrence ratesof wrinkling and shift are low when the element winding processing isperformed (see paragraphs[0098] and[0099]).PRIOR ART DOCUMENT

PATENT DOCUMENTS

-   Patent Document 1: WO 2013/146367-   Patent Document 2: WO 2012/002123

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

There is a step of winding a polypropylene film for capacitor into aroll in the production process even before subjecting the film toelement winding in order to fabricate a capacitor. Specifically, in thestep of biaxially stretching an unstretched cast sheet, thepolypropylene film after being biaxially stretched is once wound into aroll. Furthermore, the polypropylene film wound into a roll in the abovestep is then rewound (unrolled), a metal layer such as a vapor-depositedfilm or the like is formed on one surface of the polypropylene film, andthe polypropylene film is wound again.

<First Object>

The present inventors have diligently carried out investigations onpolypropylene films for capacitor. As a result, it has been found outthat there is a case in which the vapor-deposited surface and thenon-vapor-deposited surface are blocked and the film wrinkles in themachine direction when the film on which a metal layer is formed isrewound even in the case of using a polypropylene film having aroughened surface in order to improve the slipperiness at the time ofelement winding processing. Incidentally, in the present description,blocking means that the upper polypropylene film and the lowerpolypropylene film which are wound and in contact with each other comecloser to each other by the pressure generated by winding, and the like.

The first present invention has been devised in light of theabove-mentioned problem, and it is an object of the first presentinvention to provide a polypropylene film which is capable ofsuppressing blocking in a rolled metal layer-integrated polypropylenefilm. It is another object of the first present invention to provide ametal layer-integrated polypropylene film including the polypropylenefilm, a film capacitor including the metal layer-integratedpolypropylene film, and a film roll in which the polypropylene film iswound into a roll.

<Second Object>

The present inventors have diligently carried out investigations onpolypropylene films for capacitor. As a result, it has been found outthat there is a case in which the vapor-deposited surface and thenon-vapor-deposited surface are blocked and the film wrinkles in themachine direction when the film on which a metal layer is formed isrewound even in the case of using a polypropylene film having aroughened surface in order to improve the slipperiness at the time ofelement winding processing. Incidentally, in the present description,blocking means that the upper polypropylene film and the lowerpolypropylene film which are wound and in contact with each other comecloser to each other by the pressure generated by winding, and the like.It has also been found out that there is a case in which the end surfaceshift (the shift length when the film meanders left and right at thetime of winding and the end surfaces of small roll are unmatched)increases when the polypropylene film is subjected to slit processing asmetal vapor deposition winding.

The second present invention has been devised in light of theabove-mentioned problem, and it is an object of the second presentinvention to provide a polypropylene film which is capable ofsuppressing blocking in a rolled metal layer-integrated polypropylenefilm. It is another object of the second present invention to provide ametal layer-integrated polypropylene film including the polypropylenefilm, a film capacitor including the metal layer-integratedpolypropylene film, and a film roll in which the polypropylene film iswound into a roll. Moreover, the second present invention still morepreferably provides a polypropylene film having excellent processabilityin the slitting step, a metal layer-integrated polypropylene filmincluding the polypropylene film, a film capacitor including the metallayer-integrated polypropylene film, and a film roll in which thepolypropylene film is wound into a roll in addition to the objectsdescribed above.

<Third Object>

The present inventors have diligently carried out investigations onpolypropylene films for capacitor. As a result, it has been found outthat there is a case in which the vapor-deposited surface and thenon-vapor-deposited surface are blocked and the film wrinkles in themachine direction when the film on which a metal layer is formed isrewound even in the case of using a polypropylene film having aroughened surface in order to improve the slipperiness at the time ofelement winding processing. Incidentally, in the present description,blocking means that the upper polypropylene film and the lowerpolypropylene film which are wound and in contact with each other comecloser to each other by the pressure generated by winding, and the like.

The third present invention has been devised in light of theabove-mentioned problem, and it is an object of the third presentinvention to provide a polypropylene film which is capable ofsuppressing blocking in a rolled metal layer-integrated polypropylenefilm. It is another object of the third present invention to provide ametal layer-integrated polypropylene film including the polypropylenefilm, a film capacitor including the metal layer-integratedpolypropylene film, and a film roll in which the polypropylene film iswound into a roll.

Means for Solving the Problems First Present Invention

The present inventors have diligently carried out investigations on theabove findings in order to achieve the first object. As a result, thepresent inventors have found out that it is possible to suppressblocking in a rolled polypropylene film by adopting the followingconstitution, and completed the first present invention.

The polypropylene film according to the first present invention is apolypropylene film having a first surface and a second surface, in whichthe polypropylene film contains a polypropylene resin as a maincomponent;

-   -   a Svk value (Svk_(A)) of the first surface is 0.005 μm or more        and 0.030 μm or less;    -   a Spk value (Spk_(A)) of the first surface is more than 0.035 μm        and 0.080 μm or less;    -   a Svk value (Svk_(B)) of the second surface is 0.005 μm or more        and 0.030 μm or less; and    -   a Spk value (Spk_(B)) of the second surface is 0.015 μm or more        and 0.035 μm or less.

Here, the Svk value and the Spk value are parameters defined by thesurface quality parameter (ISO 25178-2: 2007). The Svk value refers tothe average height of the protruding valley portions below the curveattained by removing the protruding hill portions and the protrudingvalley portions from the bearing curve. The Spk value refers to theaverage height of the protruding hill portions above the curve attainedby removing the protruding hill portions and the protruding valleyportions from the bearing curve.

The polypropylene film includes a metal layer formed on either or bothof the first surface and the second surface, and the first surface andthe second surface are in contact with each other in a state in whichthe metal layer formed thereon when the polypropylene film is wound.According to the configuration, the Spk value (Spk_(A)) of the firstsurface, the Spk value (Spk_(A)) of the first surface, the Svk value(Svk_(B)) of the second surface, and the Spk value (Spk_(B)) of thesecond surface are within the numerical ranges and both surfaces of thepolypropylene film are roughened. In addition, on the assumption thatboth surfaces are roughened, the degrees of roughening are differentfrom each other within the numerical ranges. Hence, the contact areabetween the first surface and the second surface when the polypropylenefilm is wound decreases, the gaps between the first surface and thesecond surface due to moderate coarse protrusions can be maintained, andexcellent cushioning property is exhibited. As a result, it is possibleto suppress blocking as can be seen from Examples as well.

In addition, the polypropylene film is generally wound by using aplurality of conveying rolls while applying tension to the polypropylenefilm in order not to cause wrinkling and meandering. Therefore, not onlyone surface touches the conveying rolls, but the winding is performedwhile both surfaces touch one of the conveying rolls.

According to the configuration, both surfaces of the polypropylene filmare roughened and thus the slipperiness with respect to the conveyingrolls is suitable on both surfaces when the polypropylene film afterbeing biaxially stretched is wound into a roll. As a result, suitableconveying property is attained, wrinkling and winding shift aresuppressed, and the element winding processability is improved.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Hereinafter, this point will be described.

In general, the thickness of the film is such that the apex of theconvex portion is the end portion of the thickness in a case in whichthere are irregularities on the surface. In other words, in a case inwhich there are irregularities on both the first surface and the secondsurface, the distance from the apex of the convex portion present on thefirst surface to the apex of the convex portion present on the secondsurface is the film thickness.

Here, the thickness of the core portion is the thickness attained bysubtracting the height of the convex portion of the first surface andthe height of the convex portion of the second surface. Hence, when apolypropylene film of which both surfaces are roughened is fabricated,the thickness of the core portion is thin, a leakage current is likelyto be generated, and the dielectric strength decreases.

Consequently, the first present invention is configured to moderatelyroughen both surfaces by setting (1) the Svk value (Svk_(A)) of thefirst surface and the Svk value (Svk_(B)) of the second surface to beabout the same, namely, the depths of the valley portions to be aboutthe same on the first surface and the second surface and to ensure thethickness of the core portion by setting (2) the Spk value (Spk_(B)) ofthe second surface to be smaller than the Spk value (Spk_(A)) of thefirst surface for the coarse protrusions. In this manner, the conveyingproperty due to roughening is exhibited while the dielectric strength ismaintained.

As described above, according to the first present invention, it ispossible to suppress blocking and further to achieve both the conveyingproperty and dielectric strength.

A polypropylene film having the configuration is preferably for use incapacitor.

A polypropylene film in which the Spk value (Spk_(A)) of the firstsurface, the Spk value (Spk_(A)) of the first surface, the Svk value(Svk_(B)) of the second surface, and the Spk value (Spk_(B)) of thesecond surface are within the numerical ranges can suppress blocking,further has both conveying property and dielectric strength, and thuscan be suitably used for capacitors.

A polypropylene film having the configuration is preferably biaxiallystretched.

When the polypropylene film is biaxially stretched, it is easy tofabricate a polypropylene film in which the Spk value (Spk_(A)) of thefirst surface, the Spk value (Spk_(A)) of the first surface, the Svkvalue (Svk_(B)) of the second surface, and the Spk value (Spk_(B)) ofthe second surface are within the numerical ranges.

In the polypropylene film having the configuration, it is preferred thatthe ratio Sq_(B)/Sq_(A) of the Sq value (Sq_(B)) of the second surfaceto the Sq value (Sq_(A)) of the first surface is 0.4 to 1.0.

Here, the Sq value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the value of the root mean square of theheight data in the defined region.

When the ratio Sq_(B)/Sq_(A) is 0.4 to 1.0, blocking after the formationof metal layer can be suppressed while the dielectric breakdown strengthis maintained. As a result, it is preferred since it leads tosuppression of wrinkling at the time of feeding in the subsequentslitting step.

In the polypropylene film having the configuration, it is preferred thatthe ratio Sa_(B)/Sa_(A) of the Sa value (Sa_(B)) of the second surfaceto the Sa value (Sa_(A)) of the first surface is 0.6 to 1.0.

Here, the Sa value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the arithmetic mean value of the absolutevalues of the height data in the defined region.

When the ratio Sa_(B)/Sa_(A) is 0.6 to 1.0, the amounts of airassociated with the run of film become closer to each other on the frontand back. As a result, it is preferred since meandering of the film issuppressed and this leads to suppression of end surface shift of smallroll in the slitting step of the metal layer-integrated film.

In the polypropylene film having the configuration,

-   -   it is preferred that the polypropylene resin contains    -   a linear polypropylene resin A having a difference (a difference        when a differential distribution value when Log (M)=6.0 is 100%        (basis), hereinafter also referred to as “differential        distribution value difference D_(M)”) of 8.0% or more attained        by subtracting a differential distribution value when a        logarithmic molecular weight Log (M)=6.0 from a differential        distribution value when a logarithmic molecular weight Log        (M)=4.5 in a molecular weight differential distribution curve;    -   a linear polypropylene resin B having a difference (differential        distribution value difference D_(M)) of less than 8.0% attained        by subtracting a differential distribution value when a        logarithmic molecular weight Log (M)=6.0 from a differential        distribution value when a logarithmic molecular weight Log        (M)=4.5 in a molecular weight differential distribution curve;        and    -   a long-chain branched polypropylene resin C polymerized using a        metallocene catalyst.

To contain the linear polypropylene resin A and linear polypropyleneresin B which have different differential distribution values from eachother means to contain two kinds of linear polypropylene resins in whichthe quantitative relation between the higher molecular weight componentand the lower molecular weight component are different from each other.Therefore, the nonoriented polypropylene film (cast sheet) containingthe linear polypropylene resin A and the linear polypropylene resin B isin a finely mixed state (phase separated state). It is considered thatthe dielectric strength at high temperatures is improved as comparedwith a case in which one kind of linear polypropylene resin is usedsingly since the arrangement of the resin components constituting thefilm is complicated by stretching such a nonoriented polypropylene film.

In addition, the present inventors have discovered that a large amountof β crystal is formed in the specific cast sheet when the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis contained. Moreover, the present inventors have discovered that the βcrystal is transformed into a crystal by stretching the cast sheetcontaining the β crystal, thus (substantially) arc-shaped irregularitiesare formed on the polypropylene film obtained by stretching due to thedifference in density between the β crystal and the α crystal, and thesurface can be suitably roughened.

Incidentally, by containing the long-chain branched polypropylene resinC polymerized using a metallocene catalyst as well as containing thelinear polypropylene resin A and linear polypropylene resin B which havedifferent differential distribution values from each other, it ispossible to improve the dielectric strength of the oriented film by thecomplicated arrangement of the resin components constituting the film,to form finer (substantially) arc-shaped irregularities, and to realizemore suitable roughening.

In this manner, when the polypropylene film contains the linearpolypropylene resin A, the linear polypropylene resin B, and thelong-chain branched polypropylene resin C, it is possible to realizemore suitable roughening while achieving more suitable dielectricstrength at high temperatures.

Incidentally, when a long-chain branched polypropylene resin obtainedthrough crosslinking modification by a peroxide is used instead of thelong-chain branched polypropylene resin C polymerized using ametallocene catalyst, the α crystal formation is promoted in the castsheet and the β crystal formation is greatly suppressed by the α crystalnucleation effect of the long-chain branched polypropylene resinobtained through crosslinking modification by a peroxide. Even when thecast sheet containing α crystal is stretched, the transfer ofcrystallites does not occur and thus irregularities are hardly formed.Hence, in order to roughen the polypropylene film, the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis suitable.

In addition, the metal layer-integrated polypropylene film according tothe first present invention includes the polypropylene film; and

-   -   a metal layer stacked on either surface or both surfaces of the        polypropylene film.

According to the configuration, the film includes a metal layer stackedon either surface or both surfaces of the polypropylene film and thuscan be used in a film capacitor including a polypropylene film as adielectric and a metal layer as an electrode. In addition, blocking inthe polypropylene film is suppressed, further both conveying propertyand dielectric strength are achieved, and thus the metallayer-integrated polypropylene film including the polypropylene film canbe suitably produced and has dielectric strength.

In addition, the film capacitor according to the first present inventionincludes the metal layer-integrated polypropylene film that is wound orhas a configuration in which a plurality of the metal layer-integratedpolypropylene films are stacked.

In addition, in the film roll according to the first present invention,the polypropylene film is wound into a roll.

The first present invention has been described above.

Second Present Invention

The present inventors have diligently carried out investigations on theabove findings in order to achieve the second object. As a result, thepresent inventors have found out that it is possible to suppressblocking in a rolled polypropylene film by adopting the followingconstitution, and completed the second present invention. In addition,it has been found out that the processability in the slitting step isalso excellent as a preferred case by adopting the followingconfiguration.

The polypropylene film according to the second present invention is apolypropylene film having a first surface and a second surface, in which

-   -   the polypropylene film contains a polypropylene resin as a main        component;    -   a ratio Spk_(B)/Spk_(A) of a Spk value (Spk_(B)) of the second        surface to a Spk value (Spk_(A)) of the first surface is 0.490        or more and 0.730 or less, and    -   a ratio Svk_(B)/Svk_(A) of a Svk value (Svk_(B)) of the second        surface to a Svk value (Svk_(A)) of the first surface is 0.735        or more and 1.250 or less.

Here, the Svk value and the Spk value are parameters defined by thesurface quality parameter (ISO 25178-2: 2007). The Svk value refers tothe average height of the protruding valley portions below the curveattained by removing the protruding hill portions and the protrudingvalley portions from the bearing curve. The Spk value refers to theaverage height of the protruding hill portions above the curve attainedby removing the protruding hill portions and the protruding valleyportions from the bearing curve.

The polypropylene film includes a metal layer formed on either or bothof the first surface and the second surface, and the first surface andthe second surface are in contact with each other in a state in whichthe metal layer formed thereon when the polypropylene film is wound.According to the configuration, the ratios attained using the Spk value(Spk_(A)) of the first surface, the Spk value (Spk_(A)) of the firstsurface, the Svk value (Svk_(B)) of the second surface, and the Spkvalue (Spk_(B)) of the second surface are within the numerical rangesand the degrees of surface roughening are different from each otherwithin the numerical ranges. Hence, the contact area between the firstsurface and the second surface when the polypropylene film is wounddecreases, the gaps between the first surface and the second surface dueto moderate coarse protrusions can be maintained, and excellentcushioning property is exhibited. As a result, it is possible tosuppress blocking as can be seen from Examples as well. In addition,according to the configuration, the processability in the slitting stepis also excellent as a preferred case.

In addition, the polypropylene film is generally wound by using aplurality of conveying rolls while applying tension to the polypropylenefilm in order not to cause wrinkling and meandering. Therefore, not onlyone surface touches the conveying rolls, but the winding is performedwhile both surfaces touch one of the conveying rolls.

According to the configuration, both surfaces of the polypropylene filmare roughened to about an equal degree and thus the slipperiness withrespect to the conveying rolls is suitable on both surfaces when thepolypropylene film after being biaxially stretched is wound into a roll.As a result, suitable conveying property is attained, wrinkling andwinding shift are suppressed, and the element winding processability isimproved.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Hereinafter, this point will be described.

In general, the thickness of the film is such that the apex of theconvex portion is the end portion of the thickness in a case in whichthere are irregularities on the surface. In other words, in a case inwhich there are irregularities on both the first surface and the secondsurface, the distance from the apex of the convex portion present on thefirst surface to the apex of the convex portion present on the secondsurface is the film thickness.

Here, the thickness of the core portion is the thickness attained bysubtracting the height of the convex portion of the first surface andthe height of the convex portion of the second surface. Hence, when apolypropylene film of which both surfaces are roughened is fabricated,the thickness of the core portion is thin, a leakage current is likelyto be generated, and the dielectric strength decreases.

Consequently, the second present invention is configured to set (1) theSvk value (Svk_(A)) of the first surface and the Svk value (Svk_(B)) ofthe second surface to be about the same, namely, the depths of thevalley portions to be about the same on the first surface and the secondsurface and to ensure the thickness of the core portion by setting (2)the Spk value (Spk_(B)) of the second surface to be smaller than the Spkvalue (Spk_(A)) of the first surface for the coarse protrusions. In thismanner, the conveying property due to roughening is exhibited while thedielectric strength is maintained.

As described above, according to the second present invention, it ispossible to suppress blocking and further to achieve all theprocessability in the slitting step, conveying property, and dielectricstrength.

A polypropylene film having the configuration is preferably for use incapacitor.

A polypropylene film in which the Spk value (Spk_(A)) of the firstsurface, the Spk value (Spk_(A)) of the first surface, the Svk value(Svk_(B)) of the second surface, and the Spk value (Spk_(B)) of thesecond surface are within the numerical ranges can suppress blocking,further has all the processability in the slitting step, conveyingproperty, and dielectric strength, and thus can be suitably used forcapacitors.

A polypropylene film having the configuration is preferably biaxiallystretched.

When the polypropylene film is biaxially stretched, it is easy tofabricate a polypropylene film in which the Spk value (Spk_(A)) of thefirst surface, the Spk value (Spk_(A)) of the first surface, the Svkvalue (Svk_(B)) of the second surface, and the Spk value (Spk_(B)) ofthe second surface are within the numerical ranges.

In the polypropylene film having the configuration, it is preferred thatthe ratio Sq_(B)/Sq_(A) of the Sq value (Sq_(B)) of the second surfaceto the Sq value (Sq_(A)) of the first surface is 0.4 to 1.0.

Here, the Sq value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the value of the root mean square of theheight data in the defined region.

When the ratio Sq_(B)/Sq_(A) is 0.4 to 1.0, blocking after the formationof metal layer can be suppressed while the dielectric breakdown strengthis maintained. As a result, it is preferred since it leads tosuppression of wrinkling at the time of feeding in the subsequentslitting step.

In the polypropylene film having the configuration, it is preferred thatthe ratio Sa_(B)/Sa_(A) of the Sa value (Sa_(B)) of the second surfaceto the Sa value (Sa_(A)) of the first surface is 0.6 to 1.0.

Here, the Sa value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the arithmetic mean value of the absolutevalues of the height data in the defined region.

When the ratio Sa_(B)/Sa_(A) is 0.6 to 1.0, the amounts of airassociated with the run of film become closer to each other on the frontand back. As a result, it is preferred since meandering of the film issuppressed and this leads to suppression of end surface shift of smallroll in the slitting step of the metal layer-integrated film.

In the polypropylene film having the configuration,

-   -   it is preferred that the polypropylene resin contains    -   a linear polypropylene resin A having a difference (a difference        when a differential distribution value when Log (M)=6.0 is 100%        (basis), hereinafter also referred to as “differential        distribution value difference D_(M)”) of 8.0% or more attained        by subtracting a differential distribution value when a        logarithmic molecular weight Log (M)=6.0 from a differential        distribution value when a logarithmic molecular weight Log        (M)=4.5 in a molecular weight differential distribution curve;    -   a linear polypropylene resin B having a difference (differential        distribution value difference D_(M)) of less than 8.0% attained        by subtracting a differential distribution value when a        logarithmic molecular weight Log (M)=6.0 from a differential        distribution value when a logarithmic molecular weight Log        (M)=4.5 in a molecular weight differential distribution curve;        and    -   a long-chain branched polypropylene resin C polymerized using a        metallocene catalyst.

To contain the linear polypropylene resin A and linear polypropyleneresin B which have different differential distribution values from eachother means to contain two kinds of linear polypropylene resins in whichthe quantitative relation between the higher molecular weight componentand the lower molecular weight component are different from each other.Therefore, the nonoriented polypropylene film (cast sheet) containingthe linear polypropylene resin A and the linear polypropylene resin B isin a finely mixed state (phase separated state). It is considered thatthe dielectric strength at high temperatures is improved as comparedwith a case in which one kind of linear polypropylene resin is usedsingly since the arrangement of the resin components constituting thefilm is complicated by stretching such a nonoriented polypropylene film.

In addition, the present inventors have discovered that a large amountof β crystal is formed in the specific cast sheet when the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis contained. Moreover, the present inventors have discovered that the βcrystal is transformed into a crystal by stretching the cast sheetcontaining the β crystal, thus (substantially) arc-shaped irregularitiesare formed on the polypropylene film obtained by stretching due to thedifference in density between the β crystal and the α crystal, and thesurface can be suitably roughened.

Incidentally, by containing the long-chain branched polypropylene resinC polymerized using a metallocene catalyst as well as containing thelinear polypropylene resin A and linear polypropylene resin B which havedifferent differential distribution values from each other, it ispossible to improve the dielectric strength of the oriented film by thecomplicated arrangement of the resin components constituting the film,to form finer (substantially) arc-shaped irregularities, and to realizemore suitable roughening.

In this manner, when the polypropylene film contains the linearpolypropylene resin A, the linear polypropylene resin B, and thelong-chain branched polypropylene resin C, it is possible to realizemore suitable roughening while achieving more suitable dielectricstrength at high temperatures.

Incidentally, when a long-chain branched polypropylene resin obtainedthrough crosslinking modification by a peroxide is used instead of thelong-chain branched polypropylene resin C polymerized using ametallocene catalyst, the α crystal formation is promoted in the castsheet and the β crystal formation is greatly suppressed by the α crystalnucleation effect of the long-chain branched polypropylene resinobtained through crosslinking modification by a peroxide. Even when thecast sheet containing α crystal is stretched, the transfer ofcrystallites does not occur and thus irregularities are hardly formed.Hence, in order to roughen the polypropylene film, the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis suitable.

In addition, the metal layer-integrated polypropylene film according tothe second present invention includes

-   -   the polypropylene film; and    -   a metal layer stacked on either surface or both surfaces of the        polypropylene film.

According to the configuration, the film includes a metal layer stackedon either surface or both surfaces of the polypropylene film and thuscan be used in a film capacitor including a polypropylene film as adielectric and a metal layer as an electrode. In addition, blocking inthe polypropylene film is suppressed, further all the processability inthe slitting step, conveying property, and dielectric strength areachieved, and thus the metal layer-integrated polypropylene filmincluding the polypropylene film can be suitably produced and hasdielectric strength.

In addition, the film capacitor according to the second presentinvention includes the metal layer-integrated polypropylene film that iswound or has a configuration in which a plurality of the metallayer-integrated polypropylene films are stacked.

In addition, in the film roll according to the second present invention,the polypropylene film is wound into a roll.

The second present invention has been described above.

Third Present Invention

The present inventors have diligently carried out investigations on theabove findings in order to achieve the third object. As a result, thepresent inventors have found out that it is possible to suppressblocking in a rolled polypropylene film by adopting the followingconstitution, and completed the third present invention.

The polypropylene film according to the third present invention is apolypropylene film having a first surface and a second surface, in which

-   -   the polypropylene film contains a polypropylene resin as a main        component;    -   an ellipse density D_(A) on the first surface is 85 to 120        pieces/mm²; and    -   an ellipse density D_(B) on the second surface is 1 to 12        pieces/mm².

Both surfaces of the polypropylene film are roughened by crater-likefine irregularities. FIG. 1(a) is a perspective view schematicallyillustrating crater-like fine irregularities, FIG. 1(b) is across-sectional view of the crater-like fine irregularities, and FIG.1(c) is a vertical cross-sectional view taken along line I-I′ in FIG.1(b). Incidentally, FIG. 1(a) to FIG. 1(c) are schematic views forexplaining an “ellipse” but do not illustrate the surface shape of thepolypropylene film or the like according to Examples to be describedlater.

Most of the crater-like fine irregularities are observed as two arcshapes or substantially arc shapes (hereinafter, the arc shape and thesubstantially arc shape are collectively referred to as “(substantially)arc shape”) which form a pair of curves which are curved in oppositedirections under, for example, an optical microscope. In a case in whichtwo (substantially) arc-shaped parts forming an observed pair arecomplemented (interpolated) and connected, the two parts form anelliptical shape or a substantially elliptical shape (hereinafter, theelliptical shape and the substantially elliptical shape are collectivelyreferred to as “(substantially) elliptical shape”).

These two (substantially) arc-shaped parts forming a pair form aprotrusion and a recess between the protrusions (see FIG. 1(a)). Theseprotrusions and recesses form the crater-like fine irregularities (seeFIGS. 1(b) and 1(c)). Incidentally, the two (substantially) arc shapesmay be combined to form a circular shape, a substantially circular shape(hereinafter, the circular shape and the substantially circular shapeare collectively referred to as “(substantially) circular shape”), or a(substantially) elliptical shape. The cross section of the protrusion inthis case becomes a circular ring or a substantially circular ring(hereinafter, the circular ring and the substantially circular ring arecollectively referred to as “(substantially) circular ring”) or anelliptical ring or a substantially elliptical ring (hereinafter, theelliptical ring and the substantially elliptical ring are collectivelyreferred to as “(substantially) elliptical ring”). In addition, thearc-shaped parts are observed as a single (substantially) arc shapewithout forming a pair in some cases.

The ellipse density refers to the total number of the following (X) and(Y) observed using a digital scope (for example, Digital MicroscopeVHX-2000 available from Keyence Corporation) per unit area. Hereinafter,the shape of the following (X) and the shape of the following (Y) arealso collectively referred to as “ellipse”.

Incidentally, those satisfying S≤L and 1≤L≤300, where the length of oneaxis is denoted as L μm and the length of the other axis is denoted as Sμm, are defined as “ellipses” to be considered when the ellipse densityis calculated. Those that do not satisfy this are not considered whenthe ellipse density is calculated (not counted as “ellipses” when theellipse density is calculated).

(X) A (substantially) circular shape or (substantially) elliptical shapeformed by combining two (substantially) arc-shaped protrusions formingthe above pair.

(Y) A (substantially) elliptical shape formed by interpolating andconnecting the two (substantially) arc shapes forming the pair.

The ellipse density D_(A) on the first surface is 85 to 120 pieces/mm²and the ellipse density D_(B) on the second surface is 1 to 12pieces/mm², thus the contact area between the first surface and thesecond surface when the polypropylene film is wound decreases, the gapbetween the first surface and the second surface can be maintained dueto the difference in ellipse density, and excellent cushioning propertyis exhibited. As a result, it is possible to suppress blocking as can beseen from Examples as well.

In addition, the ellipse density D_(A) on the first surface is 85 to 120pieces/mm² and it can be said that the number of “ellipses” isrelatively large. Hence, the surface is roughened to a greater degree.Meanwhile, the ellipse density D_(B) on the second surface is 1 to 12pieces/mm² and it can be said that the number of “ellipses” isrelatively small. Hence, the degree of roughening is low although thesurface is roughened.

It is possible to prevent the film from meandering to left and right inthe slit processing and the end surfaces of small roll from beingunmatched if the ellipse density D_(A) on the first surface is set to 85to 120 pieces/mm² and the ellipse density D_(B) on the second surface isset to 1 to 12 pieces/mm² in this manner. As a result, it is possible toimprove the processability in the slitting step as can be seen fromExamples as well.

In addition, the polypropylene film is generally wound by using aplurality of conveying rolls while applying tension to the polypropylenefilm in order not to cause wrinkling and meandering. Therefore, not onlyone surface touches the conveying rolls, but the winding is performedwhile both surfaces touch one of the conveying rolls.

According to the polypropylene film, both surfaces of the polypropylenefilm are roughened and thus the slipperiness with respect to theconveying rolls is suitable on both surfaces when the polypropylene filmafter being biaxially stretched is wound into a roll. As a result,suitable conveying property is attained and wrinkling and winding shiftare suppressed.

Specifically, the ellipse density D_(A) on the first surface is 85 to120 pieces/mm² and the ellipse density D_(B) on the second surface is 1to 12 pieces/mm², thus both surfaces of the polypropylene film aresuitably roughened, and thus the slipperiness with respect to theconveying rolls is suitable on both surfaces when the polypropylene filmafter being biaxially stretched is wound into a roll. As a result,suitable conveying property is attained, wrinkling and winding shift arefurther suppressed, and the element winding processability is improved.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Generally, when the surface is roughened, thin parts (concave portionsof irregularities) of the film cause leakage current. Hence, it ispossible to diminish the number of irregularities that may cause leakagecurrent if the ellipse density D_(B) on the second surface is set to belower than the ellipse density D_(A) on the first surface. Specifically,it can be said that the number of irregularities that may cause leakagecurrent is small when the ellipse density D_(B) on the second surface is1 to 12 pieces/mm². As a result, a configuration is attained in whichmore suitable conveying property due to roughening is exhibited whilethe dielectric strength is suitably maintained.

As described above, according to the third present invention, it ispossible to suppress blocking and further to achieve all theprocessability in the slitting step, conveying property, and dielectricstrength.

A polypropylene film having the configuration is preferably for use incapacitor.

A polypropylene film in which the ellipse density D_(A) on the firstsurface is 85 to 120 pieces/mm² and the ellipse density D_(B) on thesecond surface is 1 to 12 pieces/mm² can suppress blocking, further hasall the processability in the slitting step, conveying property, anddielectric strength, and thus can be suitably used for capacitors.

A polypropylene film having the configuration is preferably biaxiallystretched.

When the polypropylene film is biaxially stretched, it is easy tofabricate a polypropylene film in which the ellipse density D_(A) on thefirst surface is 85 to 120 pieces/mm² and the ellipse density D_(B) onthe second surface is 1 to 12 pieces/mm².

In the polypropylene film having the configuration, it is preferred thatthe average major axis length LA of the ellipses constituting theellipse density D_(A) on the first surface is 20 to 80 μm and theaverage major axis length L_(B) of the ellipses constituting the ellipsedensity D_(B) on the second surface is 30 to 100 μm.

The average major axis length LA is an average value of major axes ofthe “ellipses” observed in the measurement of the ellipse density D_(A).

The average major axis length L_(B) is an average value of major axes ofthe “ellipses” observed in the measurement of the ellipse density D_(B).

When the average major axis length LA of the ellipses constituting theellipse density D_(A) on the first surface is 20 to 80 μm, it is easy toset the ellipse density D_(A) on the first surface to be within thenumerical range. In addition, when the average major axis length L_(B)of the ellipses constituting the ellipse density D_(B) on the secondsurface is 30 to 100 μm, it is easy to set the ellipse density D_(B) onthe second surface to be within the numerical range.

In the polypropylene film having the configuration, it is preferred thatthe ratio Sq_(B)/Sq_(A) of the Sq value (Sq_(B)) of the second surfaceto the Sq value (Sq_(A)) of the first surface is 0.4 to 1.0.

Here, the Sq value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the value of the root mean square of theheight data in the defined region.

When the ratio Sq_(B)/Sq_(A) is 0.4 to 1.0, blocking after the formationof metal layer can be suppressed while the dielectric breakdown strengthis maintained. As a result, it is preferred since it leads tosuppression of wrinkling at the time of feeding in the subsequentslitting step.

In the polypropylene film having the configuration, it is preferred thatthe ratio Sa_(B)/Sa_(A) of the Sa value (Sa_(B)) of the second surfaceto the Sa value (Sa_(A)) of the first surface is 0.6 to 1.0.

Here, the Sa value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the arithmetic mean value of the absolutevalues of the height data in the defined region.

When the ratio Sa_(B)/Sa_(A) is 0.6 to 1.0, the amounts of airassociated with the run of film become closer to each other on the frontand back. As a result, it is preferred since meandering of the film issuppressed and this leads to suppression of end surface shift of smallroll in the slitting step of the metal layer-integrated film.

In the polypropylene film having the configuration,

-   -   it is preferred that the polypropylene resin contains    -   a linear polypropylene resin A having a difference (a difference        when a differential distribution value when Log (M)=6.0 is 100%        (basis), hereinafter also referred to as “differential        distribution value difference D_(M)”) of 8.0% or more attained        by subtracting a differential distribution value when a        logarithmic molecular weight Log (M)=6.0 from a differential        distribution value when a logarithmic molecular weight Log        (M)=4.5 in a molecular weight differential distribution curve;    -   a linear polypropylene resin B having a difference (differential        distribution value difference D_(M)) of less than 8.0% attained        by subtracting a differential distribution value when a        logarithmic molecular weight Log (M)=6.0 from a differential        distribution value when a logarithmic molecular weight Log        (M)=4.5 in a molecular weight differential distribution curve;        and    -   a long-chain branched polypropylene resin C polymerized using a        metallocene catalyst.

To contain the linear polypropylene resin A and linear polypropyleneresin B which have different differential distribution values from eachother means to contain two kinds of linear polypropylene resins in whichthe quantitative relation between the higher molecular weight componentand the lower molecular weight component are different from each other.Therefore, the nonoriented polypropylene film (cast sheet) containingthe linear polypropylene resin A and the linear polypropylene resin B isin a finely mixed state (phase separated state). It is considered thatthe dielectric strength at high temperatures is improved as comparedwith a case in which one kind of linear polypropylene resin is usedsingly since the arrangement of the resin components constituting thefilm is complicated by stretching such a nonoriented polypropylene film.

In addition, the present inventors have discovered that a large amountof β crystal is formed in the specific cast sheet when the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis contained. Moreover, the present inventors have discovered that the βcrystal is transformed into a crystal by stretching the cast sheetcontaining the β crystal, thus (substantially) arc-shaped irregularitiesare formed on the polypropylene film obtained by stretching due to thedifference in density between the β crystal and the α crystal, and thesurface can be suitably roughened.

Incidentally, by containing the long-chain branched polypropylene resinC polymerized using a metallocene catalyst as well as containing thelinear polypropylene resin A and linear polypropylene resin B which havedifferent differential distribution values from each other, it ispossible to improve the dielectric strength of the oriented film by thecomplicated arrangement of the resin components constituting the film,to form finer (substantially) arc-shaped irregularities, and to realizemore suitable roughening.

In this manner, when the polypropylene film contains the linearpolypropylene resin A, the linear polypropylene resin B, and thelong-chain branched polypropylene resin C, it is possible to realizemore suitable roughening while achieving more suitable dielectricstrength at high temperatures.

Incidentally, when a long-chain branched polypropylene resin obtainedthrough crosslinking modification by a peroxide is used instead of thelong-chain branched polypropylene resin C polymerized using ametallocene catalyst, the α crystal formation is promoted in the castsheet and the β crystal formation is greatly suppressed by the α crystalnucleation effect of the long-chain branched polypropylene resinobtained through crosslinking modification by a peroxide. Even when thecast sheet containing α crystal is stretched, the transfer ofcrystallites does not occur and thus irregularities are hardly formed.Hence, in order to roughen the polypropylene film, the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis suitable.

In addition, the metal layer-integrated polypropylene film according tothe third present invention includes the polypropylene film; and

-   -   a metal layer stacked on either surface or both surfaces of the        polypropylene film.

According to the configuration, the film includes a metal layer stackedon either surface or both surfaces of the polypropylene film and thuscan be used in a film capacitor including a polypropylene film as adielectric and a metal layer as an electrode. In addition, blocking inthe polypropylene film is suppressed, further all the processability inthe slitting step, conveying property, and dielectric strength areachieved, and thus the metal layer-integrated polypropylene filmincluding the polypropylene film can be suitably produced and hasdielectric strength.

In addition, the film capacitor according to the third present inventionincludes the metal layer-integrated polypropylene film that is wound orhas a configuration in which a plurality of the metal layer-integratedpolypropylene films are stacked.

In addition, in the film roll according to the third present invention,the polypropylene film is wound into a roll.

The third present invention has been described above.

Effect of the Invention

According to the first present invention, it is possible to provide apolypropylene film which is capable of suppressing blocking in a rolledmetal layer-integrated polypropylene film. It is also possible toprovide a metal layer-integrated polypropylene film including thepolypropylene film, a film capacitor including the metallayer-integrated polypropylene film, and a film roll in which thepolypropylene film is wound into a roll.

According to the second present invention, it is possible to provide apolypropylene film which is capable of suppressing blocking in a rolledmetal layer-integrated polypropylene film. It is also possible toprovide a metal layer-integrated polypropylene film including thepolypropylene film and a film capacitor including the metallayer-integrated polypropylene film. Moreover, according to the secondpresent invention, it is possible to still more preferably provide apolypropylene film having excellent processability in the slitting step,a metal layer-integrated polypropylene film including the polypropylenefilm, and a film capacitor including the metal layer-integratedpolypropylene film in addition to the objects described above.

According to the third present invention, it is possible to provide apolypropylene film which is capable of suppressing blocking in a rolledmetal layer-integrated polypropylene film. It is also possible toprovide a metal layer-integrated polypropylene film including thepolypropylene film, a film capacitor including the metallayer-integrated polypropylene film, and a film roll in which thepolypropylene film is wound into a roll.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view schematically illustrating crater-likefine irregularities, FIG. 1B is a cross-sectional view of thecrater-like fine irregularities, and FIG. 1C is a verticalcross-sectional view taken along line I-I′ in FIG. 1B.

FIG. 2 is a diagram illustrating an example of a projection imageacquired by projecting parts having a height of 0.02 μm or more amongfine irregularities onto the film surface using an optical interferencetype non-contact surface shape measuring instrument.

FIGS. 3A, 3B and 3C are schematic plan views for explaining a method fordetermining a virtual circular ring. FIG. 3A shows two points farthestfrom each other on arcs 30 a and 30 b denoted as P₁ and P₂ and astraight line P₁-P₂ connecting P₁ and P.

FIG. 3B shows an ellipse (E₀) derived from the shape of the arcs 30 aand 30 b at the part located on the upper side of the straight lineP₁-P₂ by the least-squares method so that the straight line P₁-P₂becomes the major axis.

FIG. 3C shows an ellipse (E₁) derived from the shape of the arcs 30 aand 30 b at the part located on the lower side of the straight lineP₁-P₂ of the straight line P₁-P₂ by the least-squares method so that thestraight line P₁-P₂ becomes the major axis.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention (first presentinvention, second present invention, and third present invention) willbe described. It is to be noted that the present invention (firstpresent invention, second present invention, and third presentinvention) is not limited only to these embodiments.

In the present description, the expressions “containing” and “including”include the concepts of “containing”, “including”, “consistingsubstantially of” and “consisting only of”.

In the present description, the terms “element”, “capacitor”, “capacitorelement”, and “film capacitor” mean the same one.

The biaxially-oriented polypropylene film of the embodiments of thepresent invention (first present invention, second present invention,and third present invention) is not a microporous film and thus does nothave a large number of pores.

The biaxially-oriented polypropylene film of the embodiments of thepresent invention (first present invention, second present invention,and third present invention) may be formed of two or more layers but ispreferably formed of one layer.

Embodiment According to First Present Invention

Hereinafter, an embodiment of the first present invention will bedescribed.

The polypropylene film according to an embodiment (hereinafter, alsoreferred to as “first embodiment”) according to the first presentinvention is a polypropylene film contains a polypropylene resin as amain component, and

-   -   in the polypropylene film    -   the Svk value (Svk_(A)) of the first surface is 0.005 μm or more        and 0.030 μm or less,    -   the Spk value (Spk_(A)) of the first surface is more than 0.035        μm and 0.080 μm or less,    -   the Svk value (Svk_(B)) of the second surface is 0.005 μm or        more and 0.030 μm or less, and    -   the Spk value (Spk_(B)) of the second surface is 0.015 μm or        more and 0.035 μm or less.

The Svk value (Svk_(A)) of the first surface is preferably 0.007 μm ormore and 0.025 μm or less, more preferably 0.008 μm or more and 0.020 μmor less, further preferably 0.009 μm or more and 0.015 μm or less.

The Spk value (Spk_(A)) of the first surface is preferably 0.040 μm ormore and 0.075 μm or less, more preferably 0.043 μm or more and 0.060 μmor less, further preferably 0.045 μm or more and 0.055 μm or less.

The Svk value (Svk_(B)) of the second surface is preferably 0.007 μm ormore and 0.025 μm or less, more preferably 0.008 μm or more and 0.020 μmor less, further preferably 0.009 μm or more and 0.015 μm or less.

The Spk value (Spk_(B)) of the second surface is preferably 0.017 μm ormore and 0.033 μm or less, more preferably 0.018 μm or more and 0.030 μmor less, further preferably 0.020 μm or more and 0.025 μm or less.

The polypropylene film includes a metal layer formed on either or bothof the first surface and the second surface, and the first surface andthe second surface are in contact with each other in a state in whichthe metal layer formed thereon when the polypropylene film is wound.According to the polypropylene film, the Spk value (Spk_(A)) of thefirst surface, the Spk value (Spk_(A)) of the first surface, the Svkvalue (Svk_(B)) of the second surface, and the Spk value (Spk_(B)) ofthe second surface are within the numerical ranges and both surfaces ofthe polypropylene film are roughened. In addition, on the assumptionthat both surfaces are roughened, the degrees of roughening aredifferent from each other within the numerical ranges. Hence, thecontact area between the first surface and the second surface when thepolypropylene film is wound decreases, the gaps between the firstsurface and the second surface due to moderate coarse protrusions can bemaintained, and excellent cushioning property is exhibited. As a result,it is possible to suppress blocking as can be seen from Examples aswell.

In addition, the polypropylene film is generally wound by using aplurality of conveying rolls while applying tension to the polypropylenefilm in order not to cause wrinkling and meandering. Therefore, not onlyone surface touches the conveying rolls, but the winding is performedwhile both surfaces touch one of the conveying rolls.

According to the polypropylene film, both surfaces of the polypropylenefilm are roughened and thus the slipperiness with respect to theconveying rolls is suitable on both surfaces when the polypropylene filmafter being biaxially stretched is wound into a roll. As a result,suitable conveying property is attained, wrinkling and winding shift aresuppressed, and the element winding processability is improved.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Hereinafter, this point will be described.

In general, the thickness of the film is such that the apex of theconvex portion is the end portion of the thickness in a case in whichthere are irregularities on the surface. In other words, in a case inwhich there are irregularities on both the first surface and the secondsurface, the distance from the apex of the convex portion present on thefirst surface to the apex of the convex portion present on the secondsurface is the film thickness.

Here, the thickness of the core portion is the thickness attained bysubtracting the height of the convex portion of the first surface andthe height of the convex portion of the second surface. Hence, when apolypropylene film of which both surfaces are roughened is fabricated,the thickness of the core portion is thin, a leakage current is likelyto be generated, and the dielectric strength decreases.

Consequently, in the first embodiment, the polypropylene film isconfigured to moderately roughen both surfaces by setting (1) the Svkvalue (Svk_(A)) of the first surface and the Svk value (Svk_(B)) of thesecond surface to be about the same, namely, the depths of the valleyportions to be about the same on the first surface and the secondsurface and to ensure the thickness of the core portion by setting (2)the Spk value (Spk_(B)) of the second surface to be smaller than the Spkvalue (Spk_(A)) of the first surface for the coarse protrusions. In thismanner, the conveying property due to roughening is exhibited while thedielectric strength is maintained.

As described above, according to the polypropylene film according to thefirst embodiment, it is possible to suppress blocking and further toachieve both the conveying property and dielectric strength.

The Svk value (Svk_(A)) of the first surface, the Spk value (Spk_(A)) ofthe first surface, the Svk value (Svk_(B)) of the second surface, andthe Spk value (Spk_(B)) of the second surface are determined bymeasuring the surface shapes by a three-dimensional surface roughnessevaluation method using an optical interference type non-contact surfaceshape measuring instrument. By the “three-dimensional surface roughnessevaluation method”, the height of the entire film surface is evaluatedand thus the shape of the film surface is three-dimensionally evaluated.Hence, it is possible to grasp the local minute change or modificationof the surface to be measured and to more accurately evaluate thesurface roughness. It is possible to suppress blocking by evaluating thefilm surface roughness not simply using the heights of protrusions(two-dimensional surface roughness evaluation by general centerlineaverage roughness Ra and the like) but using the average height ofthree-dimensional protruding hill portions and average height ofprotruding valley portions. In addition, it is possible to have aconfiguration achieving both the favorable conveying property anddielectric strength.

More specifically, the Svk value (Svk_(A)) of the first surface, the Spkvalue (Spk_(A)) of the first surface, the Svk value (Svk_(B)) of thesecond surface, and the Spk value (Spk_(B)) of the second surface arevalues measured using “VertScan 2.0 (model: R5500GML)” available fromRyoka Systems, Inc. as an optical interference type non-contact surfaceshape measuring instrument.

The details of the measuring method will be described below.

First, the measurement is performed in a region of 470.92 μm×353.16 μmper one visual field at the WAVE mode by applying a 530 white filter anda 1× BODY lens tube and using an objective lens (10×). This operation isperformed at 10 positions at 1 cm intervals in the machine directionfrom the position to be the center in both the machine direction andwidth direction of the target sample (polypropylene film).

Next, the acquired data is subjected to noise removal processing by amedian filter (3×3) and then to Gaussian filter processing at a cutoffvalue of 30 μm to remove the waviness component. By this, a state isattained in which the state of the roughened surface can be properlymeasured.

Next, analysis is performed using the “ISO parameter” in the plug-infunction “Bearing” of the analysis software “VS-Viewer” of “VertScan2.0”.

Finally, the average values are each calculated for the respectivevalues (Svk_(A), Spk_(A), Svk_(B), Spk_(B), Sq_(A), Sq_(B), Sa_(A),Sa_(B), Sk_(A), and Sk_(B)) attained at the 10 positions. In thismanner, the Svk value (Svk_(A)) of the first surface, the Spk value(Spk_(A)) of the first surface, the Svk value (Svk_(B)) of the secondsurface, and the Spk value (Spk_(B)) of the second surface are attained.In addition, Sq_(A), Sq_(B), Sa_(A), Sa_(B), Sk_(A), and Sk_(B) are alsoattained in the same manner.

More specifically, the method described in Examples is adopted.

In the polypropylene film, the ratio Sq_(B)/Sq_(A) of the Sq value(Sq_(B)) of the second surface to the Sq value (Sq_(A)) of the firstsurface is preferably 0.4 to 1.0, more preferably 0.45 to 0.8, furtherpreferably 0.48 to 0.7.

The Sq_(A) is preferably 0.020 μm to 0.080 μm, more preferably 0.025 μmto 0.070 μm.

The Sq_(B) is preferably 0.005 μm to 0.030 μm, more preferably 0.010 μmto 0.025 μm.

When the ratio Sq_(B)/Sq_(A) is 0.4 to 1.0, blocking after the formationof metal layer can be suppressed while the dielectric breakdown strengthis maintained. As a result, it is preferred since it leads tosuppression of wrinkling at the time of feeding in the subsequentslitting step.

The detailed method for measuring the Sq value (Sq_(A)) of the firstsurface, the Sq value (Sq_(B)) of the second surface, and the ratioSq_(B)/Sq_(A) follows the method described in Examples.

In the polypropylene film, the ratio Sa_(B)/Sa_(A) of the Sa value(Sa_(B)) of the second surface to the Sa value (Sa_(A)) of the firstsurface is preferably 0.6 to 1.0, more preferably 0.65 to 0.9, furtherpreferably 0.7 to 0.8.

The Sa_(A) is preferably 0.005 μm to 0.025 μm, more preferably 0.009 μmto 0.020 μm.

The Sa_(B) is preferably 0.005 μm to 0.025 μm, more preferably 0.007 μmto 0.015 μm.

When the ratio Sa_(B)/Sa_(A) is 0.6 to 1.0, the amounts of airassociated with the run of film become closer to each other on the frontand back. As a result, it is preferred since meandering of the film issuppressed and this leads to suppression of end surface shift of smallroll in the slitting step of the metal layer-integrated film.

The detailed method for measuring the Sa value (Sa_(A)) of the firstsurface, the Sa value (Sa_(B)) of the second surface, and the ratioSa_(B)/Sa_(A) follows the method described in Examples.

In the polypropylene film, the ratio Sk_(B)/Sk_(A) of the Sk value(Sk_(B)) of the second surface to the Sk value (Sk_(A)) of the firstsurface and is preferably 0.6 to 1.0, more preferably 0.7 to 0.9,further preferably 0.75 to 0.85.

The Sk_(A) is preferably 0.030 μm to 0.070 μm, more preferably 0.035 to0.060.

The Sk_(B) is preferably 0.010 μm to 0.050 μm, more preferably 0.020 μmto 0.040 μm.

Here, the Sk value is a parameter defined by a surface quality parameter(ISO 25178-2: 2007) and is the difference between the upper level andthe lower level in the curve attained by removing the protruding hillportions and the protruding valley portions from the bearing curve.

When the ratio Sk_(B)/Sk_(A) is 0.6 to 1.0, blocking after the formationof metal layer can be suppressed while the dielectric breakdown strengthis maintained. As a result, it is preferred since it leads tosuppression of wrinkling at the time of feeding in the subsequentslitting step.

The detailed method for measuring the Sk value (Sk_(A)) of the firstsurface, the Sk value (Sk_(B)) of the second surface, and the ratioSk_(B)/Sk_(A) follows the method described in Examples.

The method for setting the Svk value (Svk_(A)) of the first surface, theSpk value (Spk_(A)) of the first surface, the Svk value (Svk_(B)) of thesecond surface, the Spk value (Spk_(B)) of the second surface, the Sqvalue (Sq_(A)) of the first surface, the Sq value (Sq_(B)) of the secondsurface, the ratio Sq_(B)/Sq_(A), the Sa value (Sa_(A)) of the firstsurface, the Sa value (Sa_(B)) of the second surface, the ratioSa_(B)/Sa_(A), the Sk value (Sk_(A)) of the first surface, the Sk value(Sk_(B)) of the second surface, and the ratio Sk_(B)/Sk_(A) to be withinthe numerical ranges is not particularly limited, but these values canbe appropriately adjusted by (i) the selection of the kinds,stereoregularity, molecular weight distribution, and differentialdistribution value difference D_(M) of resins (raw material resins)constituting the polypropylene film, (ii) the contents of the respectiveresins with respect to the entire polypropylene film, (iii) the stretchratios in the longitudinal and transverse directions at the time ofstretching and the stretching temperature, (iv) the selection of thekinds of additives (particularly nucleating agent) and the contentsthereof, and the like.

The method for setting the Svk value (Svk_(A)) of the first surface andthe Svk value (Svk_(B)) of the second surface to be different from eachother, the method for settiating the Spk value (Spk_(A)) of the firstsurface and the Spk value (Spk_(B)) of the second surface to bedifferent from each other, the method for setting the Sq value (Sq_(A))of the first surface and the Sq value (Sq_(B)) of the second surface tobe different from each other, the method for setting the Sa value(Sa_(A)) of the first surface and the Sa value (Sa_(B)) of the secondsurface to be different from each other, and the method for setting theSk value (Sk_(A)) of the first surface and the Sk value (Sk_(B)) of thesecond surface to be different from each other are not particularlylimited, but these values can be adjusted by, for example, fabricating acast sheet with the first surface as the cast roll side surface and thesecond surface as the air knife side surface and biaxially stretchingthis cast sheet.

Both surfaces of the polypropylene film may be roughened by crater-likefine irregularities. FIG. 1(a) is a perspective view schematicallyillustrating crater-like fine irregularities, FIG. 1(b) is across-sectional view of the crater-like fine irregularities, and FIG.1(c) is a vertical cross-sectional view taken along line I-I′ in FIG.1(b). Incidentally, FIG. 1(a) to FIG. 1(c) are schematic views forexplaining an “ellipse” but do not illustrate the surface shape of thepolypropylene film or the like according to Examples to be describedlater.

Most of the crater-like fine irregularities are observed as two arcshapes or substantially arc shapes (hereinafter, the arc shape and thesubstantially arc shape are collectively referred to as “(substantially)arc shape”) which form a pair of curves which are curved in oppositedirections under, for example, an optical microscope. In a case in whichtwo (substantially) arc-shaped parts forming an observed pair arecomplemented (interpolated) and connected, the two parts form anelliptical shape or a substantially elliptical shape (hereinafter, theelliptical shape and the substantially elliptical shape are collectivelyreferred to as “(substantially) elliptical shape”).

These two (substantially) arc-shaped parts forming a pair form aprotrusion and a recess between the protrusions (see FIG. 1(a)). Theseprotrusions and recesses form the crater-like fine irregularities (seeFIGS. 1(b) and 1(c)). Incidentally, the two (substantially) arc shapesmay be combined to form a circular shape, a substantially circular shape(hereinafter, the circular shape and the substantially circular shapeare collectively referred to as “(substantially) circular shape”), or a(substantially) elliptical shape. The cross section of the protrusion inthis case becomes a circular ring or a substantially circular ring(hereinafter, the circular ring and the substantially circular ring arecollectively referred to as “(substantially) circular ring”) or anelliptical ring or a substantially elliptical ring (hereinafter, theelliptical ring and the substantially elliptical ring are collectivelyreferred to as “(substantially) elliptical ring”). In addition, thearc-shaped parts are observed as a single (substantially) arc shapewithout forming a pair in some cases.

In the polypropylene film, it is preferred that the ellipse densityD_(A) on the first surface is 85 to 120 pieces/mm² and the ellipsedensity D_(B) on the second surface is 1 to 12 pieces/mm².

The ellipse density D_(A) is more preferably 85 to 110 pieces/mm²,further preferably 90 to 105 pieces/mm².

The ellipse density D_(B) is more preferably 3 to 11 pieces/mm², furtherpreferably 4 to 10 pieces/mm².

The ellipse density refers to the total number of the following (X) and(Y) observed using a digital scope (for example, Digital MicroscopeVHX-2000 available from Keyence Corporation) per unit area. Hereinafter,the shape of the following (X) and the shape of the following (Y) arealso collectively referred to as “ellipse”.

Incidentally, those satisfying S≤L and 1≤L≤300, where the length of oneaxis is denoted as L μm and the length of the other axis is denoted as Sμm, are defined as “ellipses” to be considered when the ellipse densityis calculated. Those that do not satisfy this are not considered whenthe ellipse density is calculated (not counted as “ellipses” when theellipse density is calculated).

(X) A (substantially) circular shape or (substantially) elliptical shapeformed by combining two (substantially) arc-shaped protrusions formingthe above pair.

(Y) A (substantially) elliptical shape formed by interpolating andconnecting the two (substantially) arc shapes forming the pair.

The specific method for measuring the ellipse density follows the methoddescribed in Examples.

When the ellipse density D_(A) on the first surface is 85 to 120pieces/mm² and the ellipse density D_(B) on the second surface is 1 to12 pieces/mm², it is possible to further decrease the contact areabetween the first surface and the second surface when the polypropylenefilm is wound.

Specifically, when the ellipse density D_(A) on the first surface is 85to 120 pieces/mm², it can be said that the number of “ellipses” isrelatively large. Hence, the surface is roughened to a greater degree.Meanwhile, when the ellipse density D_(B) on the second surface is 1 to12 pieces/mm², it can be said that the number of “ellipses” isrelatively small. Hence, the degree of roughening is low although thesurface is roughened.

It is possible to prevent the film from meandering to left and right inthe slit processing and the end surfaces of small roll from beingunmatched if the ellipse density D_(A) on the first surface is set to 85to 120 pieces/mm² and the ellipse density D_(B) on the second surface isset to 1 to 12 pieces/mm² in this manner. As a result, it is possible toimprove the processability in the slitting step as can be seen fromExamples as well.

In addition, when the ellipse density D_(A) on the first surface is 85to 120 pieces/mm² and the ellipse density D_(B) on the second surface is1 to 12 pieces/mm², both surfaces of the polypropylene film are moresuitably roughened, and thus the slipperiness with respect to theconveying rolls is more suitable on both surfaces when the polypropylenefilm after being biaxially stretched is wound into a roll. As a result,more suitable conveying property is attained and wrinkling and windingshift are further suppressed.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Generally, when the surface is roughened, thin parts (concave portionsof irregularities) of the film cause leakage current. Hence, it ispossible to diminish the number of irregularities that may cause leakagecurrent if the ellipse density D_(B) on the second surface is set to belower than the ellipse density D_(A) on the first surface. Specifically,it can be said that the number of irregularities that may cause leakagecurrent is small when the ellipse density D_(B) on the second surface is1 to 12 pieces/mm². As a result, a configuration is attained in whichconveying property due to roughening is more suitably exhibited whilethe dielectric strength is more suitably maintained.

In the polypropylene film, it is preferred that the average major axislength LA of the ellipses constituting the ellipse density D_(A) on thefirst surface is 20 to 80 μm and the average major axis length L_(B) ofthe ellipses constituting the ellipse density D_(B) on the secondsurface is 30 to 100 μm.

The average major axis length LA is more preferably 30 to 70 μm, furtherpreferably 40 to 68 μm.

The average major axis length L_(B) is more preferably 35 to 90 μm,further preferably 40 to 80 μm.

The average major axis length LA is an average value of major axes ofthe “ellipses” observed in the measurement of the ellipse density D_(A).

The average major axis length L_(B) is an average value of major axes ofthe “ellipses” observed in the measurement of the ellipse density D_(B).

The specific method for measuring the average major axis length LA andthe average major axis length L_(B) follows the method described inExamples.

When the average major axis length LA of the ellipses constituting theellipse density D_(A) on the first surface is 20 to 80 μm, it is easy toset the ellipse density D_(A) on the first surface to be within thenumerical range. In addition, when the average major axis length L_(B)of the ellipses constituting the ellipse density D_(B) on the secondsurface is 30 to 100 μm, it is easy to set the ellipse density D_(B) onthe second surface to be within the numerical range.

In the polypropylene film, it is preferred that the ellipse perfectnessPA of the ellipses constituting the ellipse density D_(A) on the firstsurface is 30% to 70% and the ellipse perfectness PB of the ellipsesconstituting the ellipse density D_(B) on the second surface is 15% to50%.

The ellipse perfectness PA is more preferably 35% to 65%, furtherpreferably 40% to 60%.

The ellipse perfectness PB is more preferably 20% to 45%, furtherpreferably 25% to 40%.

The ellipse perfectness is a value determined as follows.

First, surface shape data in a region of 470.92 μm×353.16 μm per onevisual field is acquired at the WAVE mode by applying a 530 white filterand a 1× BODY lens tube and using an objective lens (10×) and “VertScan2.0 (model: R5500GML)” available from Ryoka Systems, Inc. as an opticalinterference type non-contact surface shape measuring instrument. Thisoperation is performed at 10 positions at 1 cm intervals in the machinedirection from the position to be the center in both the machinedirection and width direction of the target sample (polypropylene film).

Next, the acquired data is subjected to noise removal processing by amedian filter (3×3) and then to Gaussian filter processing at a cutoffvalue of 30 μm to remove the waviness component.

Three crater projection images each consisting of paired arcs areextracted from each of the projection images of surface shape data at 10positions acquired as described above (see FIG. 2 ).

FIG. 2 is a diagram illustrating an example of a projection imageacquired by projecting parts having a height of 0.02 μm or more amongfine irregularities onto the film surface using an optical interferencetype non-contact surface shape measuring instrument. Incidentally, FIG.2 is an image illustrated in order to facilitate visual understanding ofthe “projection image” but is not a projection image of thepolypropylene film or the like according to Examples to be describedlater.

When extracting crater projection images, three crater projection imagesin which arcs based on different β-spherulites are not acknowledged tooverlap each other are extracted. As the method for extracting threecrater projection images, the ellipses which become the quartiles (firstquartile, second quartile (namely, median value), and third quartile) inthe area of ellipse by visual observation are extracted. For example, ina case in which N crater projection images are confirmed, the craterprojection images having the [(3+N)/4]th largest area, the [(1+N)/2]thlargest area, and the [(1+3N)/4]th largest area are extracted as thefirst quartile, the second quartile, and the third quartile,respectively. In a case in which the first quartile to the thirdquartile attained by substituting N have a decimal point, the numbersafter the decimal point are rounded off so that the first quartile tothe third quartile are integers. Specifically, for example, in a case inwhich 9 crater projection images are confirmed, the crater projectionimages having the 3rd, 5th, and 7th areas are extracted. In addition,for example, in a case in which 12 crater projection images areconfirmed, the crater projection images having the 4th, 7th, and 9thareas are extracted.

Next, for each of the three extracted crater projection images, thetotal length Lt of the paired arcs and the total circumferential lengthLc of the virtual circular ring including the paired arcs are measuredto determine the ratio (Lt/Lc). Thereafter, the values of the ratio fortotal 30 images thus attained are averaged to attain the average value aof the ratio (Lt/Lc).

The determination of virtual circular ring and the measurement of Lt andLc are performed using the plug-in function “edge curve length” of theanalysis software “VS-Viewer” of the optical interference typenon-contact surface shape measuring instrument VertScan 2.0. Thespecific procedure is as follows.

FIGS. 3A, 3B and 3C are schematic plan views for explaining a method fordetermining a virtual circular ring.

(1) First, two points farthest from each other on arcs 30 a and 30 b aredenoted as P₁ and P₂ and a straight line (hereinafter, referred to asstraight line (P₁-P₂)) connecting P₁ and P₂ is determined as illustratedin FIG. 3A.

(2) Subsequently, an ellipse (E₀) is derived from the shape (locationdata) of the arcs 30 a and 30 b at the part located on one side (theupper side of the straight line (P₁-P₂) in FIG. 3A) of the straight line(P₁-P₂) by the least-squares method so that the straight line (P₁-P₂)becomes the major axis as illustrated in FIG. 3B. Thereafter, the curve(a part of the circumference of the ellipse (E₀)) constituting thisellipse (E₀) complements the part between the arcs 30 a and 30 b on theone side to form a complementary line 40 a. Incidentally, the ellipse(E₀) is not illustrated except for the part corresponding to thecomplementary line 40 a in FIG. 3B.

(3) Subsequently, an ellipse (E₁) is derived from the shape (locationdata) of the arcs 30 a and 30 b at the part located on the other side(the lower side of the straight line (P₁-P₂) in FIG. 3A) of the straightline (P₁-P₂) by the least-squares method so that the straight line(P₁-P₂) becomes the major axis as illustrated in FIG. 3C. Thereafter,the curve (a part of the circumference of the ellipse (E₁)) constitutingthis ellipse (E₁) complements the part between the arcs 30 a and 30 b onthe other side to form a complementary line 40 b. Incidentally, theellipse (E₁) is not illustrated except for the part corresponding to thecomplementary line 40 b in FIG. 3C.

(4) The circular ring which is connected by the complementary lines 40 aand 40 b thus determined and the arcs 30 a and 30 b and illustrated inFIG. 3C is a virtual circular ring.

(5) Thereafter, a height profile of fine irregularities 20 is drawnwhich indicates the heights of the fine irregularities 20 at therespective locations with respect to the respective locations (distanceswhen a point on the circumference is used as the basis) on thecircumference of this virtual circular ring. Lt and Lc in a craterprojection image G corresponding to the part having a height of 0.02 μmor more are read out from this height profile.

Incidentally, 30 pieces (n=30) of location data are used for each whenthe least-squares method is carried out.

When the ellipse perfectness PA is 40% to 60% and the ellipseperfectness PB is 25% to 35%, blocking after the formation of metallayer can be suppressed while the dielectric breakdown strength ismaintained. As a result, it is preferred since it leads to suppressionof wrinkling at the time of feeding in the subsequent slitting step.

The direct current dielectric breakdown strength ES of the polypropylenefilm at 100° C. is preferably 510 V_(DC)/μm or more, more preferably 525V_(DC)/μm or more, further preferably 540 V_(DC)/μm or more. It is morepreferred as the direct current dielectric breakdown strength ES of thepolypropylene film at 100° C. is higher, but ES is, for example, 600V_(DC)/μm or less, 570 V_(DC)/μm or less, or 550 V_(DC)/μm or less.

The direct current dielectric breakdown strength ES of the polypropylenefilm at 120° C. is preferably 485 V_(DC)/μm or more, more preferably 490V_(DC)/μm or more. It is more preferred as the direct current dielectricbreakdown strength ES of the polypropylene film at 120° C. is higher,but ES is, for example, 600 V_(DC)/μm or less or 550 V_(DC)/μm or less.

The ash content in the polypropylene film is preferably 6×10 ppm or less(60 ppm or less), more preferably 5×10 ppm or less (50 ppm or less),further preferably 4×10 ppm or less (40 ppm or less), especiallypreferably 3×10 ppm or less (30 ppm or less) with respect to thepolypropylene film. The ash content is preferably 0×10 ppm or more, morepreferably 1 ppm or more, further preferably 5 ppm or more, especiallypreferably 1×10 ppm or more (10 ppm or more). When the ash content iswithin the numerical range, the electric characteristics as a capacitorare further improved while the generation of polar low molecular weightcomponents is suppressed. The ash content refers to a value attained bythe method described in Examples.

The thickness of the polypropylene film is preferably 9.5 μm or less,more preferably 6.0 μm or less, further preferably 3.0 μm or less, yetfurther preferably 2.9 μm or less, especially preferably 2.8 μm or less,yet especially preferably 2.5 μm or less. In addition, the thickness ofthe polypropylene film is preferably 0.8 μm or more, more preferably 1.0μm or more, further preferably 1.4 μm or more, yet further preferably1.5 μm or more, especially preferably 1.8 μm or more. In particular, itis preferred that the thickness is within the range of 1.4 to 6.0 μm,1.5 to 3.0 μm, 1.5 to 2.9 μm, and the like since the polypropylene filmhas excellent processability in the slitting step, blockingsuppressibility at the time of the vapor deposition step, and elementwinding processability although the polypropylene film is significantlythin.

When the thickness is 9.5 μm or less, it is possible to increase thecapacitance and thus to suitably use the polypropylene film for acapacitor. In addition, the thickness can be set to be 0.8 μm or morefrom the viewpoint of production.

The thickness of the polypropylene film means a value measured inaccordance with JIS-C2330 except that the measurement is performed at100±10 kPa using a paper thickness measuring device MEI-11, availablefrom Citizen Seimitsu Co., Ltd.

The polypropylene film may be a biaxially-oriented film, auniaxially-oriented film, or a nonoriented film. Among these, thepolypropylene film is a biaxially-oriented film from the viewpoint ofeasily setting the Spk value (Spk_(A)) of the first surface, the Spkvalue (Spk_(A)) of the first surface, the Svk value (Svk_(B)) of thesecond surface, and the Spk value (Spk_(B)) of the second surface to bewithin the numerical ranges.

The polypropylene film and the metal layer-integrated polypropylene filmare each wound into a roll and preferably in the form of a film roll.The film roll may or may not have a winding core (core). The film rollpreferably has a winding core (core). The material for the winding coreof the film roll is not particularly limited. Examples of the materialinclude paper (paper tube), resin, fiber reinforced plastic (FRP), andmetal. Examples of the resin include polyvinyl chloride, polyethylene,polypropylene, phenol resin, epoxy resin, andacrylonitrile-butadiene-styrene copolymer. Examples of the plasticconstituting the fiber reinforced plastic include polyester resin, epoxyresin, vinyl ester resin, phenol resin, and thermoplastic resin.Examples of the fiber constituting the fiber reinforced plastic includeglass fiber, aramid fiber (Kevlar (registered trademark) fiber), carbonfiber, polyparaphenylene benzoxazole fiber (Zylon (registered trademark)fiber), polyethylene fiber, and boron fiber. Examples of the metalinclude iron, aluminum, and stainless steel. The winding core of thefilm roll also includes a winding core formed by impregnating a papertube with the resin. In this case, the material for the winding core isclassified as resin.

As described above, the polypropylene film contains a polypropyleneresin as the main component. In the present description, to contain apolypropylene resin as a main component means to contain a polypropyleneresin at 50% by mass or more with respect to the entire polypropylenefilm (when the entire polypropylene film is 100% by mass). The contentof the polypropylene resin with respect to the entire polypropylene filmis preferably 75% by mass or more, more preferably 90% by mass or more.The upper limit of the content of the polypropylene resin is, forexample, 100% by mass, 98% by mass and the like with respect to theentire polypropylene film.

The polypropylene resin is not particularly limited, and one kind may beused singly or two or more kinds may be used in combination. Amongthese, the polypropylene resin is preferably a polypropylene resin whichforms β-spherulites when being formed into a cast sheet.

Examples of the polypropylene resin include a linear polypropyleneresin. The linear polypropylene resin can be used singly or in mixtureof two or more kinds thereof. Among these, it is preferred to use thefollowing linear polypropylene resin A and/or the following linearpolypropylene resin B. In particular, it is preferred to use thefollowing linear polypropylene resin A and the following linearpolypropylene resin B in combination. The following linear polypropyleneresin A and the following linear polypropylene resin B are preferablyhomopolypropylene resins. Suitable examples of the combination of thefollowing linear polypropylene resin A and the following linearpolypropylene resin B include a combination of the following resin A-1and the following resin B-1, a combination of the following resin A-2and the following resin B-2, a combination of the following resin A-3and the following resin B-3, and a combination of the following resinA-4 and the following resin B-4. However, in the first the presentinvention, the polypropylene resin is not limited to the followingresins.

<Linear Polypropylene Resin A> (Linear Polypropylene Resin A-1)

Linear polypropylene resin in which the difference attained bysubtracting the differential distribution value when the logarithmicmolecular weight Log (M)=6.0 from the differential distribution valuewhen the logarithmic molecular weight Log (M)=4.5 is 8.0% or more whenthe differential distribution value when Log (M)=6.0 is 100% (basis) inthe molecular weight differential distribution curve.

(Linear Polypropylene Resin A-2)

Linear polypropylene resin having heptane insolubles (HI) of 98.5% orless.

(Linear Polypropylene Resin A-3)

Linear polypropylene resin having melt flow rate (MFR) of 4.0 to 10.0g/10 min at 230° C.

(Linear Polypropylene Resin A-4)

Linear polypropylene resin having weight average molecular weight Mw of340,000 or less.

<Linear Polypropylene Resin B> (Linear Polypropylene Resin B-1)

Linear polypropylene resin in which the difference attained bysubtracting the differential distribution value when the logarithmicmolecular weight Log (M)=6.0 from the differential distribution valuewhen the logarithmic molecular weight Log (M)=4.5 is less than 8.0% whenthe differential distribution value when Log (M)=6.0 is 100% (basis) inthe molecular weight differential distribution curve.

(Linear Polypropylene Resin B-2)

Linear polypropylene resin having heptane insolubles (HI) of more than98.5%.

(Linear Polypropylene Resin B-3)

Linear polypropylene resin having melt flow rate (MFR) of less than 4.0g/10 min at 230° C. (especially linear polypropylene resin having meltflow rate (MFR) of 0.1 to 3.9 g/10 min).

(Linear Polypropylene Resin B-4)

Linear polypropylene resin having weight average molecular weight Mw ofmore than 340,000.

The weight average molecular weight Mw of the linear polypropylene resinA is preferably 250,000 or more. In addition, the weight averagemolecular weight Mw of the linear polypropylene resin A is preferably450,000 or less, more preferably 400,000 or less, further preferably350,000 or less, especially preferably 340,000 or less. When the weightaverage molecular weight Mw of the linear polypropylene resin A is250,000 or more and 450,000 or less, the resin fluidity is moderate. Asa result, the thickness of the cast sheet can be easily controlled, anda thin oriented film can be easily fabricated. In addition, it ispreferred that the weight average molecular weight Mw of the linearpolypropylene resin A is within the range since unevenness in thethickness of the cast sheet and oriented film is less likely to occurand moderate stretchability is attained.

The molecular weight distribution [(weight average molecular weightMw)/(number average molecular weight Mn)] of the linear polypropyleneresin A is preferably 5.5 or more and 12.0 or less, more preferably 7.0or more and 12.0 or less, further preferably 7.5 or more and 11.0 orless, especially preferably 8.0 or more and 11.0 or less, yet especiallypreferably 9.0 or more and 11.0 or less.

The molecular weight distribution [(z average molecular weightMz)/(number average molecular weight Mn)] of the linear polypropyleneresin A is preferably 15.0 or more and 70.0 or less, more preferably20.0 or more and 60.0 or less, further preferably 25.0 or more and 50.0or less.

It is preferred that the respective molecular weight distributions ofthe linear polypropylene resin A are within the preferred ranges sinceunevenness in the thickness of the cast sheet and oriented film is lesslikely to occur and moderate stretchability is attained.

In the present description, the weight average molecular weight (Mw),the number average molecular weight (Mn), the z average molecularweight, and the molecular weight distribution (Mw/Mn and Mz/Mn) of thelinear polypropylene resin A and linear polypropylene resin B are valuesmeasured by using a gel permeation chromatograph (GPC) device. In thepresent description, these are values measured by using HLC-8121GPC-HT(trade name) available from TOSOH CORPORATION, which is a hightemperature GPC measuring machine incorporating a differentialrefractometer (RI). As a GPC column, three TSKgel GMHHR-H(20)HTavailable from TOSOH CORPORATION are connected and used. Measured valuesof Mw and Mn are attained by setting the column temperature to 140° C.and allowing trichlorobenzene as an eluent to flow at a flow rate of 1.0ml/10 min. A calibration curve regarding molecular weight M is createdusing standard polystyrene available from TOSOH CORPORATION, andmeasured values are converted into the molecular weight of polypropyleneusing the Q-factor to attain Mw, Mn, and Mz. Furthermore, the logarithmwith base 10 of molecular weight M is referred to as logarithmicmolecular weight (“Log (M)”).

In addition, the weight average molecular weight (Mw), the numberaverage molecular weight (Mn), the z average molecular weight, and themolecular weight distribution (Mw/Mn and Mz/Mn) of the long-chainbranched polypropylene C are values measured by using a gel permeationchromatograph (GPC) device. More specifically, these are measured byhigh temperature GPC-MALS, that is, using a high temperature GPC device(HLC-8121GPC/HT available from TOSOH CORPORATION) equipped with a lightscattering detector (DAWN EOS available from Wyatt TechnologyCorporation). As the column, TSKgel guard column HHR (30) (7.8 mm ID×7.5cm) and three TSKgelGMH-HR-H(20)HT (7.8 mm ID×30 cm) that are allavailable from TOSOH CORPORATION are connected and used. Measured valuesof Mw and Mn are attained by setting the column temperature to 140° C.and allowing trichlorobenzene as an eluent to flow at a flow rate of 1.0ml/min.

The differential distribution value difference D_(M) of the linearpolypropylene resin A is preferably 8.0% or more, more preferably 8.0%or more and 18.0% or less, further preferably 9.0% or more and 17.0% orless, especially preferably 10.0% or more and 16.0% or less.

The fact that the differential distribution value difference D_(M) ofthe linear polypropylene resin A is 8.0% or more and 18.0% or less canbe understood to mean that the lower molecular weight component iscontained in a more amount by a proportion of 8.0% or more and 18.0% orless when a component having a logarithmic molecular weight Log (M)=4.5as a representative distribution value of a component (hereinafter, alsoreferred to as “lower molecular weight component”) having a molecularweight of from 10,000 to 100,000 on the lower molecular weight side anda component having a logarithmic molecular weight of around Log (M)=6.0as a representative distribution value of a component (hereinafter, alsoreferred to as “higher molecular weight component”) having a molecularweight of around 1,000,000 on the higher molecular weight side arecompared with each other.

In other words, for example, a case in which the molecular weightdistribution Mw/Mn is 7.0 to 12.0 is taken as an example, the molecularweight distribution Mw/Mn being 7.0 to 12.0 merely indicates the breadthof the molecular weight distribution width, and the quantitativerelation between the higher molecular weight component and the lowermolecular weight component therein is not recognized. Hence, the linearpolypropylene resin A contains a component having a molecular weight offrom 10,000 to 100,000 in a larger amount than a component having amolecular weight of 1,000,000 by a proportion of 8.0% or more and 18.0%or less.

The linear polypropylene resin A contains a lower molecular weightcomponent in a larger amount than a higher molecular weight component bya proportion of 8.0% or more and 18.0% or less in a case in which thedifferential distribution value difference D_(M) is 8.0% or more and18.0% or less. Therefore, it is preferred since the surface of the filmin the first embodiment is likely to be obtained.

The differential distribution value is a value attained in the followingmanner by using GPC. A curve is used which indicates the intensityversus time (generally, also referred to as “elution curve”) and isattained by using a differential refractometer (RI) detector of GPC. Byconverting the time axis into the logarithmic molecular weight (Log (M))by using the calibration curve attained using standard polystyrene, theelution curve is converted into a curve indicating intensity versus Log(M). Since the RI detection intensity is proportional to the componentconcentration, an integral distribution curve with respect to thelogarithmic molecular weight Log (M) can be attained by letting thetotal area of the curve indicating intensity be 100%. The differentialdistribution curve is attained by differentiating this integraldistribution curve by Log (M). Therefore, “differential distribution”means the differential distribution of concentration fraction withrespect to the molecular weight. From this curve, a differentialdistribution value at a specific Log (M) is read out.

The mesopentad fraction ([mmmm]) of the linear polypropylene resin A ispreferably 99.8% or less, more preferably 99.5% or less, furtherpreferably 99.0% or less. In addition, the mesopentad fraction ispreferably 94.0% or more, more preferably 94.5% or more, furtherpreferably 95.0% or more. When the mesopentad fraction is within thenumerical range, the crystallinity of resin is moderately improved bythe moderately high stereoregularity and the dielectric strength at hightemperatures is improved. On the other hand, the speed of solidification(crystallization) at the time of cast sheet formation is moderate andmoderate stretchability is exhibited.

The mesopentad fraction ([mmmm]) is an index for stereoregularity thatcan be attained by high temperature nuclear magnetic resonance (NMR)measurement. In the present description, the mesopentad fraction([mmmm]) refers to a value measured by using a high temperature typeFourier transformation nuclear magnetic resonance apparatus (hightemperature FT-NMR) JNM-ECP500 available from JEOL Ltd. The observationnucleus is ¹³C (125 MHz), the measurement temperature is 135° C., ando-dichlorobenzene (ODCB: mixed solvent (mixing ratio=4/1) of ODCB anddeuterated ODCB) is used as a solvent for dissolving the polypropyleneresin. The measuring method by high temperature NMR can be performed,for example, by referring to the method described in “Kobunshi BunsekiHandbook, New edition, The Japan Society for Analytical chemistry ed.,KINOKUNIYA COMPANY LTD, 1995, p. 610”. A more specific method formeasuring the mesopentad fraction ([mmmm]) follows the method describedin Examples.

The heptane insolubles (HI) in the linear polypropylene resin A ispreferably 96.0% or more, more preferably 97.0% or more. In addition,the heptane insolubles (HI) in the linear polypropylene resin A ispreferably 99.5% or less, more preferably 98.5% or less, furtherpreferably 98.0% or less. Here, the more the heptane insolubles, thehigher the stereoregularity of the resin is meant. When the heptaneinsolubles (HI) are 96.0% or more and 99.5% or less, the crystallinityof resin is moderately improved by the moderately high stereoregularityand the dielectric strength under high temperature is improved. On theother hand, the speed of solidification (crystallization) at the time ofcast sheet formation is moderate and moderate stretchability isexhibited. The method for measuring the heptane insolubles (HI) followsthe method described in Examples.

The ash content in the linear polypropylene resin A is preferably 6×10ppm or less (60 ppm or less), more preferably 5×10 ppm or less (50 ppmor less), further preferably 4×10 ppm or less (40 ppm or less),especially preferably 3×10 ppm or less (30 ppm or less). In addition,the ash content in the linear polypropylene resin A is preferably 0×10ppm or more, more preferably 1 ppm or more, further preferably 5 ppm ormore, especially preferably 1×10 ppm or more (10 ppm or more). In a casein which the ash content in the linear polypropylene resin A is withinthe preferred range, the electric characteristics as a capacitor arefurther improved while the generation of polar low molecular weightcomponents is suppressed. The ash content refers to a value attained bythe method described in Examples.

The melt flow rate (MFR) of the linear polypropylene resin A at 230° C.is preferably 1.0 to 15.0 g/10 min, more preferably 2.0 to 10.0 g/10min, further preferably 4.0 to 10.0 g/10 min, especially preferably 4.3to 6.0 g/10 min. In a case in which the MFR of the polypropylene A at230° C. is within the range, the flow characteristics in the moltenstate are excellent, thus unstable flow such as melt fracture hardlyoccurs, and breakage at the time of stretching is suppressed. Therefore,the film thickness uniformity is favorable, and thus there is anadvantage that the formation of thin portion at which dielectricbreakdown easily occurs is suppressed. The method for measuring the meltflow rate follows the method described in Examples.

The content of the linear polypropylene resin A is preferably 55% bymass or more, more preferably 60% by mass or more when the totalpolypropylene resins in the polypropylene film is 100% by mass. Thecontent of the linear polypropylene resin A is preferably 99.9% by massor less, more preferably 90% by mass or less, further preferably 85% bymass or less, especially preferably 80% by mass or less when the totalpolypropylene resins in the polypropylene film is 100% by mass.

The weight average molecular weight Mw of the linear polypropylene resinB is preferably 300,000 or more, more preferably 330,000 or more,further preferably more than 340,000, yet further preferably 350,000 ormore, especially preferably more than 350,000. In addition, the weightaverage molecular weight Mw of the linear polypropylene resin B ispreferably 400,000 or less, more preferably 380,000 or less.

The molecular weight distribution [(weight average molecular weightMw)/(number average molecular weight Mn)] of the linear polypropyleneresin B is preferably 7.0 or more and 9.0 or less, more preferably 7.5or more and 8.9 or less, further preferably 7.5 or more and 8.5 or less.

The molecular weight distribution [(z average molecular weightMz)/(number average molecular weight Mn)] of the linear polypropyleneresin B is preferably 20.0 or more and 70.0 or less, more preferably25.0 or more and 60.0 or less, further preferably 25.0 or more and 50.0or less.

It is preferred that the respective molecular weight distributions ofthe linear polypropylene resin B are within the preferred ranges sinceunevenness in the thickness of the cast sheet and oriented film is lesslikely to occur and moderate stretchability is attained.

The differential distribution value difference D_(M) of the linearpolypropylene resin B is preferably less than 8.0%, more preferably−20.0% or more and less than 8.0%, further preferably −10.0% or more and7.9% or less, and especially preferably −5.0% or more and 7.5% or less.

The mesopentad fraction ([mmmm]) of the linear polypropylene resin B ispreferably less than 99.8%, more preferably 99.5% or less, furtherpreferably 99.0% or less. In addition, the mesopentad fraction ispreferably 94.0% or more, more preferably 94.5% or more, furtherpreferably 95.0% or more. When the mesopentad fraction is within thenumerical range, the crystallinity of resin is moderately improved bythe moderately high stereoregularity and the dielectric strength at hightemperatures is improved. On the other hand, the speed of solidification(crystallization) at the time of cast sheet formation is moderate andmoderate stretchability is exhibited.

The heptane insolubles (HI) in the linear polypropylene resin B ispreferably 97.5% or more, more preferably 98% or more, furtherpreferably 98.5% or more, especially preferably 98.6% or more. Inaddition, the heptane insolubles (HI) in the linear polypropylene resinB is preferably 99.5% or less, more preferably 99.0% or less.

The ash content in the linear polypropylene resin B is preferably 6×10ppm or less (60 ppm or less), more preferably 5×10 ppm or less (50 ppmor less), further preferably 4×10 ppm or less (40 ppm or less),especially preferably 3×10 ppm or less (30 ppm or less). In addition,the ash content in the linear polypropylene resin B is preferably 0×10ppm or more, more preferably 1 ppm or more, further preferably 5 ppm ormore, especially preferably 1×10 ppm or more (10 ppm or more). In a casein which the ash content in the linear polypropylene resin B is withinthe preferred range, the electric characteristics as a capacitor arefurther improved while the generation of polar low molecular weightcomponents is suppressed. The ash content refers to a value attained bythe method described in Examples.

The melt flow rate (MFR) of the linear polypropylene resin B at 230° C.is preferably 0.1 g/10 min or more. In addition, the melt flow rate(MFR) of the linear polypropylene resin B at 230° C. is preferably 6.0g/10 min or less, more preferably 5.0 g/10 min or less, furtherpreferably less than 4.0 g/10 min, especially y preferably 3.9 g/10 minor less.

In the case of using the linear polypropylene resin B as thepolypropylene resin, the content of the linear polypropylene resin B ispreferably 10% by mass or more, more preferably 15% by mass or more,further preferably 20% by mass or more when the total polypropyleneresins in the polypropylene film is 100% by mass. In the same manner,the content of the linear polypropylene resin B is preferably 45% bymass or less, more preferably 40% by mass or less when the totalpolypropylene resins in the polypropylene film is 100% by mass.

In the case of using the linear polypropylene resin A and the linearpolypropylene resin B in combination as the polypropylene resin, it ispreferred to contain the linear polypropylene resin A at 55% to 90% byweight and the linear polypropylene resin B at 45% to 10% by weight, itis more preferred to contain the linear polypropylene resin A at 60% to85% by weight and the linear polypropylene resin B at 40% to 15% byweight, it is especially preferred to contain the linear polypropyleneresin A at 60% to 80% by weight and the linear polypropylene resin B at40% to 20% by weight when the total polypropylene resins is 100% bymass.

In a case in which the polypropylene resin contains the linearpolypropylene resin A and the linear polypropylene resin B, thepolypropylene film is in a finely mixed state (phase separated state) ofthe linear polypropylene resin A and the linear polypropylene resin B,and thus the dielectric strength at high temperatures is improved.

The linear polypropylene resins can be produced by generally knownpolymerization methods. The methods are not particularly limited as longas it is possible to produce linear polypropylene resins which can beused in the polypropylene film of the first embodiment. Examples of suchpolymerization methods include gas-phase polymerization, blockpolymerization, and slurry polymerization.

Polymerization may be single-step (one step) polymerization using onepolymerization reactor or may be multi-step polymerization using atleast two or more polymerization reactors. Furthermore, polymerizationmay be performed while hydrogen or comonomer is added as a molecularweight regulator in the reactor.

As a catalyst in polymerization, a generally known Ziegler-Nattacatalyst can be used, and the catalyst is not particularly limited aslong as a polypropylene resin can be obtained. The catalyst may containa catalyst promoter component or a donor. By adjusting the catalyst andthe polymerization conditions, it is possible to control the molecularweight, molecular weight distribution, stereoregularity and the like.

The molecular weight, molecular weight distribution, differentialdistribution value difference D_(M) and the like of the linearpolypropylene resins can be adjusted by appropriately selecting, forexample, (i) the polymerization methods and the respective conditionssuch as temperature and pressure at the time of the polymerization, (ii)the forms of reactors at the time of the polymerization, (iii) thepresence or absence, kinds, and amounts of additives used, and (iv) thekinds and amounts of catalysts used.

Specifically, the molecular weight, molecular weight distribution,differential distribution value difference D_(M) and the like of thelinear polypropylene resins can be adjusted by, for example, multi-steppolymerization reaction. As the multi-step polymerization reaction, forexample, the following methods are exemplified.

First, propylene and a catalyst are supplied to the first polymerizationreactor in the first polymerization step. Hydrogen as a molecular weightregulator is mixed with these components in an amount required to attainthe required molecular weight of polymer. For example, in the case ofslurry polymerization, the reaction temperature is about 70° C. to 100°C. and the retention time is about 20 to 100 minutes. A plurality ofreactors can be used, for example, in series. In this case, thepolymerization product in the first step is continuously sent to thenext reactor together with additional propylene, catalyst, and molecularweight regulator. Subsequently the second polymerization is performed inwhich the molecular weight is adjusted to a lower molecular weight or ahigher molecular weight than that in the first polymerization step. Byadjusting the yield (production amount) in the first and secondreactors, it is possible to adjust the composition (constitution) of thehigher molecular weight component and the lower molecular weightcomponent.

In addition, the molecular weight, molecular weight distribution,differential distribution value difference D_(M) and the like of thelinear polypropylene resins can also be adjusted by peroxidativedecomposition. For example, a method by peroxidation treatment using adecomposing agent such as hydrogen peroxide or an organic peroxide canbe exemplified.

When a peroxide is added to a disintegrating polymer such aspolypropylene, a hydrogen abstraction reaction from the polymer takesplace, the generated polymer radicals are partially recombined andundergo a crosslinking reaction, but most of the radicals undergosecondary decomposition (I cleavage) and are separated into two polymershaving lower molecular weights. In other words, the decomposition of ahigher molecular weight component proceeds at a higher probability. Inthis manner, the lower molecular weight components increase and theconstitution of the molecular weight distribution can be adjusted.

In the case of adjusting the content of lower molecular weightcomponents by blending (resin mixing), it is preferred to dry-mix ormelt-mix at least two or more kinds of resins having different molecularweights. In general, a mixed system of two kinds of propylene in whichan additive resin having an average molecular weight higher or lowerthan the main resin is mixed at about 1% to 40% by mass with the mainresin is preferably utilized since the amount of lower molecular weightcomponents can be easily adjusted.

In the case of this mixing adjustment, the melt flow rate (MFR) may beused as a measure of the average molecular weight. In this case, it ispreferred that the difference in MFR between the main resin and theadditive resin is set to about 1 to 30 g/10 min from the viewpoint ofthe convenience in the adjustment.

Commercial products can also be used as the linear polypropylene resins.

The polypropylene resin preferably contains a long-chain branchedpolypropylene resin. Among the long-chain branched polypropylene resins,the long-chain branched polypropylene resin C (hereinafter, alsoreferred to as “long-chain branched polypropylene resin C”) obtained bypolymerizing propylene using a metallocene catalyst is preferred.Specifically, when the polypropylene resin contains the long-chainbranched polypropylene resin C, a large number of β crystals is formedin the cast sheet. Moreover, it is preferred in that the β crystal istransferred into α crystal by stretching the cast sheet containing the βcrystal, thus (substantially) arc-shaped irregularities are formed onthe polypropylene film obtained by stretching due to the difference indensity between the β crystal and the α crystal, and the surface can besuitably roughened.

Among these, it is more preferred that the polypropylene resin containsthe linear polypropylene resin A and the long-chain branchedpolypropylene resin C.

Furthermore, it is more preferred that the polypropylene resin containsthe linear polypropylene resin A and the linear polypropylene resin Band contains the long-chain branched polypropylene resin C. The linearpolypropylene resin A and the linear polypropylene resin B are differentfrom each other in differential distribution value D_(M), heptaneinsolubles (HI), and/or melt flow rate (MFR) and the like and are in afinely mixed state (phase separated state), and thus the arrangement ofresin components constituting the film is complicated by stretching sucha nonoriented polypropylene film. Hence, by containing the long-chainbranched polypropylene resin C as well as containing the linearpolypropylene resin A and the linear polypropylene resin B which aredifferent from each other in differential distribution value D_(M),heptane insolubles (HI), and/or melt flow rate (MFR) and the like, it ispossible to improve the dielectric strength of the oriented film by thecomplicated arrangement of the resin components constituting the film,to form finer (substantially) arc-shaped irregularities, and to realizemore suitable roughening.

Incidentally, when a long-chain branched polypropylene resin obtainedthrough crosslinking modification by a peroxide is used instead of thelong-chain branched polypropylene resin C polymerized using ametallocene catalyst, the α crystal formation is promoted in the castsheet and the β crystal formation is greatly suppressed by the α crystalnucleation effect of the long-chain branched polypropylene resinobtained through crosslinking modification by a peroxide. Even when thecast sheet containing α crystal is stretched, the transfer ofcrystallites does not occur and thus irregularities are hardly formed.Hence, in order to roughen the polypropylene film, the long-chainbranched polypropylene resin C polymerized using a metallocene catalystis suitable.

The metallocene catalyst is generally a metallocene compound which formsa polymerization catalyst which generates an olefin macromer. Thelong-chain branched polypropylene resin C obtained by polymerizingpropylene using a metallocene catalyst is preferred since the branchedchain length and branched chain spacing of polypropylene become moderateand excellent compatibility with linear polypropylene is attained. Inaddition, it is preferred since a uniform composition and a uniformsurface shape are attained. In the production of long-chain branchedpolypropylene resin C, the respective conditions other than the kindsand amounts of catalysts used, for example, (i) the polymerizationmethods and the respective conditions such as temperature and pressureat the time of the polymerization, (ii) the forms of reactors at thetime of the polymerization, and (iii) the presence or absence, kinds,and amounts of additives used can be similar to the respectiveconditions described in the section of the method for producing thelinear polypropylene resins in consideration of the molecular weight,molecular weight distribution, differential distribution valuedifference D_(M) and the like of the long-chain branched polypropyleneresin C to be produced.

The weight average molecular weight Mw of the long-chain branchedpolypropylene resin C is preferably 150,000 or more and 600,000 or less,more preferably 200,000 or more and 500,000 or less, further preferably250,000 or more and 450,000 or less, especially preferably 350,000 ormore and 420,000 or less. When the weight average molecular weight Mw ofthe long-chain branched polypropylene resin C is 150,000 or more and600,000 or less, the resin fluidity is moderate. As a result, thethickness of the cast sheet can be easily controlled, and a thinoriented film can be easily fabricated. In addition, it is preferredthat the weight average molecular weight Mw of the long-chain branchedpolypropylene resin C is within the range since unevenness in thethickness of the cast sheet and oriented film is less likely to occurand moderate stretchability is attained.

The molecular weight distribution [(weight average molecular weightMw)/(number average molecular weight Mn)] of the long-chain branchedpolypropylene resin C is preferably 1.5 or more and 4.5 or less, morepreferably 1.8 or more and 4.2 or less, further preferably 2.0 or moreand 4.0 or less, particularly preferably 2.1 or more and 3.9 or less,especially preferably 2.2 or more and 3.0 or less.

The [(z average molecular weight Mz)/(number average molecular weightMn)] of the long-chain branched polypropylene resin C is preferably 4.0or more and 9.0 or less, more preferably 4.2 or more and 8.8 or less,further preferably 4.5 or more and 8.5 or less, especially preferably5.0 or more and 8.2 or less.

The molecular weight, molecular weight distribution, differentialdistribution value difference D_(M) and the like of the long-chainbranched polypropylene resin C can be controlled by adjusting thecatalyst and polymerization conditions as described above.

The heptane insolubles (HI) in the long-chain branched polypropyleneresin C is preferably 98.0% or more, more preferably 98.2% or more,further preferably 98.5% or more. In addition, the heptane insolubles(HI) in the long-chain branched polypropylene resin C is preferably99.5% or less, more preferably 99.0% or less. In a case in which the HIin the long-chain branched polypropylene resin C is in the preferredrange, β crystals are more suitably formed in the cast sheet, and as aresult, the surface of the polypropylene film according to the firstembodiment can be suitably roughened.

The ash content in the long-chain branched polypropylene resin C ispreferably 45×10 ppm or less (450 ppm or less), more preferably 40×10ppm or less (400 ppm or less). In addition, the ash content in thelong-chain branched polypropylene resin C is preferably 0×10 ppm ormore, more preferably 1 ppm or more, yet more preferably 5 ppm or more,further preferably 1×10 ppm or more (10 ppm or more), yet furtherpreferably 10×10 ppm or more (100 ppm or more), especially preferably20×10 ppm or more (200 ppm or more). In a case in which the ash contentin the long-chain branched polypropylene resin C is in the preferredrange, β crystals are more suitably formed in the cast sheet, and as aresult, the surface of the polypropylene film according to the firstembodiment can be suitably roughened.

The melt flow rate (MFR) of the long-chain branched polypropylene resinC at 230° C. is preferably 0.1 to 12 g/10 min, more preferably 0.5 to 5g/10 min, further preferably 0.7 to 3.5 g/10 min, especially preferably1.0 to 2.2 g/10 min. In a case in which the MFR of the long-chainbranched polypropylene resin C at 230° C. is within the range, the flowcharacteristics in the molten state are excellent, thus unstable flowsuch as melt fracture hardly occurs, and breakage at the time ofstretching is suppressed. Therefore, the film thickness uniformity isfavorable, and thus there is an advantage that the formation of thinportion at which dielectric breakdown easily occurs is suppressed.

The content of the long-chain branched polypropylene resin C ispreferably 0.1% by mass or more, more preferably 0.5% by mass or more,further preferably 1% by mass or more, especially preferably 2% by massor more, more especially preferably 2.5% by mass or more when the totalpolypropylene resins in the polypropylene film is 100% by mass. Inaddition, the content of the long-chain branched polypropylene resin Cis preferably 30 mass % or less, more preferably 20 mass % or less,further preferably 10 mass % or less, especially preferably 7 mass % orless, more especially preferably 5 mass % or less when the totalpolypropylene resins in the polypropylene film is 100% by mass. Thepolypropylene film may contain one kind or two or more kinds of the longchain branched polypropylene resins C.

Examples of representative commercial products of the long-chainbranched polypropylene resin C include MFX3 and MFX6 available fromJAPAN POLYPROPYLENE CORPORATION and MFX8 available from JAPANPOLYPROPYLENE CORPORATION.

The polypropylene film may contain resins (hereinafter, also referred toas “other resins”) other than the polypropylene resins. The “otherresins” are generally resins other than the polypropylene resins whichare regarded as resins of the main component and are not particularlylimited as long as the intended polypropylene film can be obtained.Examples of the other resins include polyolefins such as polyethylene,poly(l-butene), polyisobutene, poly(l-pentene), andpoly(l-methylpentene) other than polypropylene; copolymers of α-olefinssuch as ethylene-propylene copolymer, propylene-butene copolymer, andethylene-butene copolymer; vinyl monomer-diene monomer random copolymerssuch as styrene-butadiene random copolymer; and vinyl monomer-dienemonomer-vinyl monomer random copolymers such asstyrene-butadiene-styrene block copolymer. The polypropylene film cancontain the other resins in an amount in which the intendedpolypropylene film is not adversely affected. The polypropylene film maycontain the other resins preferably at 10 parts by mass or less, morepreferably at 5 parts by mass or less with respect to 100 parts by massof the polypropylene resins. In addition, the polypropylene film maycontain the other resins preferably at 0.1 part by mass or more, morepreferably at 1 part by mass or more with respect to 100 parts by massof the polypropylene resins.

The polypropylene film may further contain at least one kind of additivein addition to the resin components. The “additives” are generallyadditives to be used in polypropylene and are not particularly limitedas long as the intended polypropylene film can be obtained. Theadditives include, for example, a nucleating agent (a crystal nucleatingagent, β crystal nucleating agent), an antioxidant, necessarystabilizers such as a chlorine absorber and an ultraviolet absorber, alubricant, a plasticizer, a flame retardant, an antistatic agent, aninorganic filler, and an organic filler. Examples of the inorganicfiller include barium titanate, strontium titanate, and aluminum oxide.In the case of using the additives, the additives can be contained in anamount in which the intended polypropylene film is not adverselyaffected.

The “nucleating agent” is generally used in polypropylene and is notparticularly limited as long as the intended polypropylene film can beobtained.

Examples of the nucleating agent include an α crystal nucleating agentwhich preferentially nucleates α crystals and a β crystal nucleatingagent which preferentially nucleates β crystals.

Examples of an organic nucleating agent among the α crystal nucleatingagents include a dispersion type nucleating agent and a dissolution typenucleating agent. Examples of the dispersion type nucleating agentinclude a phosphate metal salt-based nucleating agent, a carboxylic acidmetal salt-based nucleating agent, and a rosin metal salt-basednucleating agent. Examples of the dissolution type nucleating agentinclude a sorbitol-based nucleating agent, a nonitol-based nucleatingagent, a xylitol-based nucleating agent, and an amide-based nucleatingagent.

Examples of the β crystal nucleating agent include an amide-basednucleating agent, a di- or polycarboxylic acid metal salt-basednucleating agent, a quinacridone-based nucleating agent, an aromaticsulfonic acid-based nucleating agent, a phthalocyanine-based nucleatingagent, and a tetraoxaspiro compound-based nucleating agent.

The nucleating agent can be used by being dry-blended or melt-blendedwith the polypropylene raw materials and pelletized or can be used bybeing put into the extruder together with polypropylene pellets. Thesurface roughness of the film can be adjusted to a desired roughness byusing a nucleating agent. Examples of a representative commercialproduct of the nucleating agent include NJSTAR NU-100 available from NewJapan Chemical Co., Ltd., for example, as a β crystal nucleating agent.In a case in which the polypropylene film contains a β crystalnucleating agent, the content thereof is preferably 1 to 1000 ppm bymass, more preferably 50 to 600 ppm by mass with respect to the mass ofthe resin components (with respective to the total mass of the resincomponents).

The “antioxidant” is generally called antioxidant, used inpolypropylene, and is not particularly limited as long as the intendedpolypropylene film can be obtained. The antioxidant is generally usedfor two purposes. One purpose is to suppress thermal deterioration andoxidative deterioration in the extruder, and the other purpose is tocontribute to the suppression of deterioration in long-term use as afilm for capacitor and the improvement of capacitor performance. Theantioxidant which suppresses thermal deterioration and oxidativedeterioration in the extruder is also referred to as “primary agent”,and the antioxidant which contributes to the improvement of capacitorperformance is also referred to as “secondary agent”.

Two kinds of antioxidants may be used for these two purposes, or onekind of antioxidant may be used for these two purposes.

Examples of the primary agent include 2,6-di-tert-butyl-para-cresol(general name: BHT). The primary agent can be usually added for thepurpose of suppressing thermal deterioration and oxidative deteriorationin the extruder at the time of preparation of the polypropylene resincomposition described in the method for producing a polypropylene filmto be described later. The antioxidant added to the polypropylene resincomposition for this purpose is mostly consumed in the molding step inthe extruder and hardly remains in the film after film formation. Hence,in a case in which the polypropylene film contains the primary agent,the content thereof is usually 100 ppm by mass with respect to the massof the resin components (with respective to the total mass of the resincomponents).

Examples of the secondary agent include a hindered phenolic antioxidanthaving a carbonyl group.

A “hindered phenolic antioxidant having a carbonyl group” is usually ahindered phenolic antioxidant having a carbonyl group and is notparticularly limited as long as the intended polypropylene film can beobtained.

Examples of the hindered phenolic antioxidant having a carbonyl groupinclude triethyleneglycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] (tradename: Irganox 245),1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](trade name: Irganox 259), pentaerythrutyltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name:Irganox 1010),2,2-thio-diethylenebis[3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate](trade name: Irganox 1035),octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name:Irganox 1076), andN,N′-hexamethylenebis(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamide)(trade name: Irganox 1098), but pentaerythrutyltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] that has ahigh molecular weight, is highly compatible with polypropylene, has lowvolatility, and is excellent in heat resistance is particularlypreferred.

The polypropylene film may contain one or more kinds of hinderedphenolic antioxidants (secondary agents) having a carbonyl group for thepurpose of suppressing the deterioration that progresses with time inlong-term use. In a case in which the polypropylene film contains one ormore kinds of hindered phenolic antioxidants having a carbonyl group,the content thereof is preferably 4000 ppm by mass or more and 6000 ppmby mass or less, more preferably 4500 ppm by mass or more and 6000 ppmby mass or less with respect to the mass of the resin components (withrespective to the total mass of the resin components). The content ofhindered phenolic antioxidants having a carbonyl group in the film ispreferably 4000 ppm by mass or more and 6000 ppm by mass or less fromthe viewpoint of proper exertion of effects.

A polypropylene film containing a hindered phenolic antioxidant having acarbonyl group, which has favorable compatibility with polypropylene atthe molecular level, in an optimal specific amount range is preferredsince the long-term durability is improved.

The “chlorine absorber” is generally called chlorine absorber, used inpolypropylene, and is not particularly limited as long as the intendedpolypropylene film can be obtained. Examples of the chlorine absorberinclude metal soap such as calcium stearate. In the case of using such achlorine absorber, the chlorine absorber can be contained in an amountin which the intended polypropylene film is not adversely affected.

The polypropylene film is preferably biaxially stretched. In a case inwhich the polypropylene film is a biaxially-oriented polypropylene film,the biaxially-oriented polypropylene film can be produced by a generallyknown method for producing a biaxially-oriented polypropylene film. Thebiaxially-oriented polypropylene film can be produced, for example, byfabricating a cast sheet from a polypropylene resin composition obtainedby mixing the linear polypropylene resin A, the linear polypropyleneresin B, and the long-chain branched polypropylene resin C with otherresins, additives and the like if necessary and then biaxiallystretching the cast sheet.

<Preparation of Polypropylene Resin Composition>

The method for preparing the polypropylene resin composition is notparticularly limited, but examples thereof include a method in whichpolymerization powders or pellets of the linear polypropylene resin A,linear polypropylene resin B, and long-chain branched polypropyleneresin C are dry-blended with other resins, additives and the like ifnecessary using a mixer or the like and a method in which polymerizationpowders or pellets of the linear polypropylene resin A, linearpolypropylene resin B, and long-chain branched polypropylene resin C aresupplied to a kneader together with other resins, additives and the likeif necessary and melt-kneaded to obtain a melt-blended resincomposition.

The mixer and the kneader are not particularly limited. The kneader maybe of a monoaxial screw type, a biaxial screw type, or a multiaxial (bi-or more axial) screw type. In the case of a bi- or more axial screw typekneader, the kneading type may be co-rating or counter-rotating.

In the case of blending by melt-kneading, the kneading temperature isnot particularly limited as long as favorable kneading is achieved butis preferably in the range of 170° C. to 320° C., more preferably in therange of 200° C. to 300° C., further preferably in the range of 230° C.to 270° C. The kneader may be purged with an inert gas such as nitrogenin order to suppress deterioration of the resins during the mixing bykneading. The melt-kneaded resin can be pelletized to a proper size byusing a generally known granulator to obtain pellets of the melt-blendedresin composition.

In the preparation of the polypropylene resin composition, a primaryagent as the antioxidant described in the section of additives can beadded for the purpose of suppressing thermal deterioration and oxidativedeterioration in the extruder.

In a case in which the polypropylene resin composition contains aprimary agent, the content thereof is preferably 1000 ppm by mass to5000 ppm by mass with respect to the mass of the resin components (withrespective to the total mass of the resin components). The antioxidantfor this purpose is mostly consumed in the molding step in the extruderand hardly remains in the film after film formation.

The hindered phenolic antioxidant having a carbonyl group described inthe section of additives can be added as a secondary agent to thepolypropylene resin composition.

In a case in which the polypropylene resin composition contains thehindered phenolic antioxidant having a carbonyl group, the contentthereof is preferably 100 ppm by mass to 10,000 ppm by mass, morepreferably 5500 ppm by mass to 7,000 ppm by mass with respect to themass of the resin components (with respective to the total mass of theresin components). In the extruder, a quite amount of hindered phenolicantioxidant having a carbonyl group is also consumed.

In a case in which the polypropylene resin composition does not containa primary agent, a larger amount of hindered phenolic antioxidant havinga carbonyl group can be used. This is because the amount of hinderedphenolic antioxidant having a carbonyl group consumed in the extrudercan be increased. In a case in which the polypropylene resin compositiondoes not contain a primary agent but contains a hindered phenolicantioxidant having a carbonyl group, the content thereof is preferably6000 ppm by mass to 8000 ppm by mass with respect to the mass of theresin components (with respective to the total mass of the resincomponents).

<Fabrication of Cast Sheet>

The cast sheet can be obtained by supplying pellets of the dry-blendedresin composition and/or melt-blended resin composition prepared inadvance to the extruder, melting the pellets under heating, allowing themolten resultant to pass through a filtration filter, then melting thefiltered resultant under heating at preferably 170° C. to 320° C., morepreferably 200° C. to 300° C., melt-extruding the molten resultantthrough a T die, and cooling and solidifying the melt-extruded resultantwith at least one metal drum held at a temperature (cast temperature) ofpreferably 40° C. to 140° C., more preferably 80° C. to 140° C., furtherpreferably 90° C. to 140° C., especially preferably 90° C. to 120° C.,more especially preferably 90° C. to 105° C. At this time, it ispreferred to press the melt-extruded resin composition against the metaldrum with an air knife. Incidentally, the surface on the side that comesinto contact with the metal drum is the first surface and the surface onthe opposite side (the surface on the air knife side) is the secondsurface.

The thickness of the cast sheet is not particularly limited as long asthe intended polypropylene film can be obtained but is preferably 0.05mm to 2 mm, more preferably 0.1 mm to 1 mm.

Incidentally, polypropylene undergoes thermal deterioration (oxidativedeterioration) and shear deterioration to no small extent during thefabrication process of the cast sheet (particularly in the extruder). Itis possible to suppress the degree of progress of such deterioration,namely, changes in the molecular weight distribution andstereoregularity by nitrogen purge (suppression of oxidation) in theextruder, screw shape (shear force) in the extruder, internal shape(shearing force) of T die at the time of casting, amount of antioxidantadded (suppression of oxidation), the winding speed (extension force) atthe time of casting, and the like.

<Stretching Treatment>

The biaxially-oriented polypropylene film can be produced by subjectingthe cast sheet to a stretching treatment. A sequential biaxialstretching method is preferred as the stretching method. As thesequential biaxial stretching method, the cast sheet is first kept at atemperature of preferably 100° C. to 180° C., more preferably 140° C. to160° C., allowed to pass between rolls with different speeds to bestretched to 3 to 7 times in the machine direction, and immediatelycooled to room temperature. By properly adjusting the temperature inthis longitudinal stretching step, β crystal melts and is transformedinto a crystal, and the irregularities become apparent. Subsequently,the stretched film is guided to a tenter and preferably transverselystretched 3 to 11 times in the width direction at a temperature ofpreferably 160° C. or more, more preferably 160° C. to 180° C., thenrelaxed, subjected to thermosetting, and wound into a roll.

The film wound into a roll is subjected to an aging treatment in anatmosphere of about 20° C. to 45° C. and then slit (cut) to the desiredproduct width with a slitter or the like while being rewound (whilebeing unrolled), and the films are each wound again.

By such a stretching step, a film having excellent mechanical strengthand rigidity is obtained and a biaxially-oriented film is obtained inwhich the irregularities on the surface are further clarified and thesurfaces are finely roughened.

The polypropylene film may be subjected to a corona discharge treatmentonline or offline after end of the stretching and thermosetting steps.By performing the corona discharge treatment, it is possible to enhancethe adhesion characteristics in a postprocessing step such as a metalvapor deposition processing step. The corona discharge treatment can beperformed by a known method. It is preferred to use air, carbon dioxidegas, nitrogen gas, and any mixed gas of these as an atmospheric gas.

In order to process the polypropylene film as a capacitor, a metal layermay be stacked on either surface or both surfaces of the polypropylenefilm to obtain a metal layer-integrated polypropylene film. The metallayer functions as an electrode. As the metal used in the metal layer,elemental metals such as zinc, lead, silver, chromium, aluminum, copper,and nickel; mixtures of a plurality of the elemental metals, and alloysthereof can be used, but zinc an aluminum are preferred in considerationof environment, economy, and capacitor performance and the like.

As a method for stacking a metal layer on either surface or bothsurfaces of the polypropylene film, for example, a vacuum vapordeposition method and a sputtering method can be exemplified. From theviewpoint of producibility and economy, the vacuum vapor depositionmethod is preferred. As the vacuum vapor deposition method, a cruciblemethod or a wire method can be generally exemplified, but the method isnot particularly limited, and any suitable method can be appropriatelyselected.

The margin pattern when stacking a metal layer by vapor deposition isnot particularly limited, but it is preferred to apply a patternincluding a so-called special margin such as a fish net pattern or a Tmargin pattern on either surface of the film from the viewpoint ofimproving the characteristics such as safety of the capacitor. Thisimproves the safety and is also effective from the viewpoint ofprevention of breakage of the capacitor and a short circuit and thelike.

As a method for forming a margin, a generally known method such as atape method or an oil method can be used without any limitation.

When forming a metal layer on the polypropylene film, the polypropylenefilm wound into a roll is rewound (unrolled), a metal layer such as avapor-deposited film is formed on either surface or both surfaces of thepolypropylene film, and the polypropylene film is wound again.

A plurality of the metal layer-integrated polypropylene films can bestacked by a conventionally known method or subjected to an elementwinding processing (winding) to be formed into a film capacitor.

Specifically, a blade is placed in the center of each margin portion ofthe metal layer-integrated polypropylene film and slit processing isperformed to fabricate a take-up reel having a margin on one surfacethereof.

Here, in the polypropylene film, the Spk value (Spk_(A)) of the firstsurface, the Spk value (Spk_(A)) of the first surface, the Svk value(Svk_(B)) of the second surface, and the Spk value (Spk_(B)) of thesecond surface are within predetermined numerical ranges and thusblocking is suppressed. Hence, it is possible to prevent thepolypropylene film from blocking and wrinkling in the machine directionof the film from occurring at the time of the slitting processing.

Next, two sheets of a take-up reel with a left margin and a take-up reelwith a right margin are superposed and wound in the width direction sothat the vapor deposition part protrudes more than the margin portion(element winding processing). Next, the core material is removed fromthe wound body and the wound body is pressed. Next, external electrodesare formed on both end surfaces, and further the external electrodes areprovided with lead wires. In this manner, a wound film capacitor isobtained.

Heretofore, the first embodiment (the embodiment according to the firstpresent invention) has been described.

Embodiment According to Second Present Invention

Hereinafter, an embodiment of the second present invention will bedescribed. Incidentally, in the polypropylene film according to theembodiment of the second present invention, the Svk value (Svk_(A)) ofthe first surface is not required to be 0.005 μm or more and 0.030 μm orless as in the embodiment of the first present invention. In addition,the Spk value (Spk_(A)) of the first surface is not required to be morethan 0.035 μm and 0.080 μm or less. In addition, the Svk value (Svk_(B))of the second surface is not required to be 0.005 μm or more and 0.030μm or less. In addition, the Spk value (Spk_(B)) of the second surfaceis not required to be 0.015 μm or more and 0.035 μm or less.

The polypropylene film according to the embodiment (hereinafter, alsoreferred to as “second embodiment”) of the second present inventioncontains a polypropylene resin as a main component, and in thepolypropylene film,

-   -   a ratio Spk_(B)/Spk_(A) of a Spk value (Spk_(B)) of the second        surface to a Spk value (Spk_(A)) of the first surface is 0.490        or more and 0.730 or less, and    -   a ratio Svk_(B)/Svk_(A) of a Svk value (Svk_(B)) of the second        surface to a Svk value (Svk_(A)) of the first surface is 0.735        or more and 1.250 or less.

The ratio Spk_(B)/Spk_(A) is preferably 0.495 or more, more preferably0.500 or more, further preferably 0.505 or more. In addition, the ratioSpk_(B)/Spk_(A) is preferably 0.710 or less, more preferably 0.700 orless, further preferably 0.690 or less.

The ratio Svk_(B)/Svk_(A) is preferably 0.750 or more, more preferably0.760 or more, further preferably 0.780 or more. In addition, the ratioSvk_(B)/Svk_(A) is preferably 1.240 or less, more preferably 1.200 orless, further preferably 1.150 or less.

The Svk value (Svk_(A)) of the first surface is not limited but ispreferably 0.005 μm or more, more preferably 0.007 μm or more, furtherpreferably 0.008 μm or more, especially preferably 0.009 μm or more. Inaddition, the Svk value (Svk_(A)) of the first surface is not limitedbut is preferably 0.050 μm or less, more preferably 0.040 μm or less,further preferably 0.035 μm or less.

The Svk value (Svk_(B)) of the second surface is not limited but ispreferably 0.005 μm or more, more preferably 0.007 μm or more, furtherpreferably 0.008 μm or more, especially preferably 0.009 μm or more. Inaddition, the Svk value (Svk_(B)) of the second surface is not limitedbut is preferably 0.050 μm or less, more preferably 0.040 μm or less,further preferably 0.035 μm or less, especially preferably 0.030 μm.

The Spk value (Spk_(A)) of the first surface is not limited but ispreferably 0.030 μm or more, more preferably 0.040 μm or more, furtherpreferably 0.043 μm or more, especially preferably 0.045 μm or more. Inaddition, the Spk value (Spk_(A)) of the first surface is not limitedbut is preferably 0.090 μm or less, more preferably 0.080 μm or less,further preferably 0.075 μm or less.

The Spk value (Spk_(B)) of the second surface is not limited but ispreferably 0.010 μm or more, more preferably 0.015 μm or more, furtherpreferably 0.020 μm or more, especially preferably 0.025 μm or more. Inaddition, the Spk value (Spk_(B)) of the second surface is not limitedbut is preferably 0.060 μm or less, more preferably 0.055 μm or less,further preferably 0.050 μm or less.

The polypropylene film includes a metal layer formed on either or bothof the first surface and the second surface, and the first surface andthe second surface are in contact with each other in a state in whichthe metal layer formed thereon when the polypropylene film is wound.According to the polypropylene film, the ratios attained using the Spkvalue (Spk_(A)) of the first surface, the Spk value (Spk_(A)) of thefirst surface, the Svk value (Svk_(B)) of the second surface, and theSpk value (Spk_(B)) of the second surface are within the numericalranges and the degrees of surface roughening are different from eachother within the numerical ranges. Hence, the contact area between thefirst surface and the second surface when the polypropylene film iswound decreases, the gaps between the first surface and the secondsurface due to moderate coarse protrusions can be maintained, andexcellent cushioning property is exhibited. As a result, it is possibleto suppress blocking as can be seen from Examples as well. In addition,according to the polypropylene film, the processability in the slittingstep is also excellent as a preferred case.

In addition, the polypropylene film is generally wound by using aplurality of conveying rolls while applying tension to the polypropylenefilm in order not to cause wrinkling and meandering. Therefore, not onlyone surface touches the conveying rolls, but the winding is performedwhile both surfaces touch one of the conveying rolls.

According to the polypropylene film, both surfaces of the polypropylenefilm are roughened to about an equal degree and thus the slipperinesswith respect to the conveying rolls is suitable on both surfaces whenthe polypropylene film after being biaxially stretched is wound into aroll. As a result, suitable conveying property is attained, wrinklingand winding shift are suppressed, and the element winding processabilityis improved.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Hereinafter, this point will be described.

In general, the thickness of the film is such that the apex of theconvex portion is the end portion of the thickness in a case in whichthere are irregularities on the surface. In other words, in a case inwhich there are irregularities on both the first surface and the secondsurface, the distance from the apex of the convex portion present on thefirst surface to the apex of the convex portion present on the secondsurface is the film thickness.

Here, the thickness of the core portion is the thickness attained bysubtracting the height of the convex portion of the first surface andthe height of the convex portion of the second surface. Hence, when apolypropylene film of which both surfaces are roughened is fabricated,the thickness of the core portion is thin, a leakage current is likelyto be generated, and the dielectric strength decreases.

Consequently, in the second embodiment, the polypropylene film isconfigured to set (1) the Svk value (Svk_(A)) of the first surface andthe Svk value (Svk_(B)) of the second surface to be about the same,namely, the depths of the valley portions, which can also be said to bean index of roughening, to be about the same on the first surface andthe second surface and to ensure the thickness of the core portion bysetting (2) the Spk value (Spk_(B)) of the second surface to be smallerthan the Spk value (Spk_(A)) of the first surface for the coarseprotrusions. In this manner, the conveying property due to roughening isexhibited while the dielectric strength is maintained.

As described above, according to the polypropylene film according to thesecond embodiment, it is possible to suppress blocking and further toachieve all the processability in the slitting step, conveying property,and dielectric strength.

The Svk value (Svk_(A)) of the first surface, the Spk value (Spk_(A)) ofthe first surface, the Svk value (Svk_(B)) of the second surface, andthe Spk value (Spk_(B)) of the second surface are determined bymeasuring the surface shapes by a three-dimensional surface roughnessevaluation method using an optical interference type non-contact surfaceshape measuring instrument. By the “three-dimensional surface roughnessevaluation method”, the height of the entire film surface is evaluatedand thus the shape of the film surface is three-dimensionally evaluated.Hence, it is possible to grasp the local minute change or modificationof the surface to be measured and to more accurately evaluate thesurface roughness. It is possible to suppress blocking by evaluating thefilm surface roughness not simply using the heights of protrusions(two-dimensional surface roughness evaluation by general centerlineaverage roughness Ra and the like) but using the average height ofthree-dimensional protruding hill portions and average height ofprotruding valley portions. In addition, it is possible to have aconfiguration achieving all the favorable processability in the slittingstep, conveying property, and dielectric strength.

More specifically, the Svk value (Svk_(A)) of the first surface, the Spkvalue (Spk_(A)) of the first surface, the Svk value (Svk_(B)) of thesecond surface, and the Spk value (Spk_(B)) of the second surface arevalues measured using “VertScan 2.0 (model: R5500GML)” available fromRyoka Systems, Inc. as an optical interference type non-contact surfaceshape measuring instrument.

The details of the measuring method will be described below.

First, the measurement is performed in a region of 470.92 μm×353.16 μmper one visual field at the WAVE mode by applying a 530 white filter anda 1× BODY lens tube and using an objective lens (10×). This operation isperformed at 10 positions at 1 cm intervals in the machine directionfrom the position to be the center in both the machine direction andwidth direction of the target sample (polypropylene film).

Next, the acquired data is subjected to noise removal processing by amedian filter (3×3) and then to Gaussian filter processing at a cutoffvalue of 30 μm to remove the waviness component. By this, a state isattained in which the state of the roughened surface can be properlymeasured.

Next, analysis is performed using the “ISO parameter” in the plug-infunction “Bearing” of the analysis software “VS-Viewer” of “VertScan2.0”.

Finally, the average values are each calculated for the respectivevalues (Svk_(A), Spk_(A), Svk_(B), Spk_(B), Sq_(A), Sq_(B), Sa_(A),Sa_(B), Sk_(A), and Sk_(B)) attained at the 10 positions. In thismanner, the Svk value (Svk_(A)) of the first surface, the Spk value(Spk_(A)) of the first surface, the Svk value (Svk_(B)) of the secondsurface, and the Spk value (Spk_(B)) of the second surface are attained.In addition, Sq_(A), Sq_(B), Sa_(A), Sa_(B), Sk_(A), and Sk_(B) are alsoattained in the same manner.

More specifically, the method described in Examples is adopted.

It is preferred that the ratio Sq_(B)/Sq_(A) of the Sq value (Sq_(B)) ofthe second surface to the Sq value (Sq_(A)) of the first surface, theSq_(A), Sq_(B), the ratio Sa_(B)/Sa_(A) of the Sa value (Sa_(B)) of thesecond surface to the Sa value (Sa_(A)) of the first surface, theSa_(A), the Sa_(B), the ratio Sk_(B)/Sk_(A) of the Sk value (Sk_(B)) ofthe second surface to the Sk value (Sk_(A)) of the first surface, theSk_(A), and the Sk_(B) of the polypropylene film are within thenumerical ranges described in the section of “embodiment of firstpresent invention”. Moreover, the meanings and determining methods ofthese parameters have been described in the section of “embodiment offirst present invention”, and thus description thereof is omitted here.

The method for setting the Svk value (Svk_(A)) of the first surface, theSpk value (Spk_(A)) of the first surface, the Svk value (Svk_(B)) of thesecond surface, the Spk value (Spk_(B)) of the second surface, the ratioSpk_(B)/Spk_(A), the ratio Svk_(B)/Svk_(A), the Sq value (Sq_(A)) of thefirst surface, the Sq value (Sq_(B)) of the second surface, the ratioSq_(B)/Sq_(A), the Sa value (Sa_(A)) of the first surface, the Sa value(Sa_(B)) of the second surface, the ratio Sa_(B)/Sa_(A), the Sk value(Sk_(A)) of the first surface, the Sk value (Sk_(B)) of the secondsurface, and the ratio Sk_(B)/Sk_(A) to be within the numerical rangesis not particularly limited, but these values can be appropriatelyadjusted by (i) the selection of the kinds, stereoregularity, molecularweight distribution, and differential distribution value differenceD_(M) of resins (raw material resins) constituting the polypropylenefilm, (ii) the contents of the respective resins with respect to theentire polypropylene film, (iii) the stretch ratios in the longitudinaland transverse directions at the time of stretching and the stretchingtemperature, (iv) the selection of the kinds of additives (particularlynucleating agent) and the contents thereof, and the like.

The method for setting the Svk value (Svk_(A)) of the first surface andthe Svk value (Svk_(B)) of the second surface to be different from eachother, the method for settiating the Spk value (Spk_(A)) of the firstsurface and the Spk value (Spk_(B)) of the second surface to bedifferent from each other, the method for setting the Sq value (Sq_(A))of the first surface and the Sq value (Sq_(B)) of the second surface tobe different from each other, the method for setting the Sa value(Sa_(A)) of the first surface and the Sa value (Sa_(B)) of the secondsurface to be different from each other, and the method for setting theSk value (Sk_(A)) of the first surface and the Sk value (Sk_(B)) of thesecond surface to be different from each other are not particularlylimited, but these values can be adjusted by, for example, fabricating acast sheet with the first surface as the cast roll side surface and thesecond surface as the air knife side surface and biaxially stretchingthis cast sheet.

Both surfaces of the polypropylene film may be roughened by crater-likefine irregularities. The crater-like fine irregularities have beendescribed in the section of “embodiment of first present invention”, andthus description thereof is omitted here.

In the polypropylene film, the ellipse density D_(A) on the firstsurface is preferably 50 to 120 pieces/mm². In addition, the ellipsedensity D_(B) on the second surface is preferably lower than the D_(A).In addition, the ellipse density D_(B) on the second surface ispreferably 1 to 90 pieces/mm².

The ellipse density D_(A) is more preferably 85 to 120 pieces/mm²,further preferably 90 to 105 pieces/mm².

The ellipse density D_(B) is more preferably 1 to 12 pieces/mm², furtherpreferably 3 to 11 pieces/mm², especially preferably 4 to 10 pieces/mm².

The method for determining the ellipse density has been described in thesection of “embodiment of first present invention”, and thus descriptionthereof is omitted here.

When the ellipse density D_(A) on the first surface is 50 to 120pieces/mm² and the ellipse density D_(B) on the second surface is 1 to90 pieces/mm², it is possible to further decrease the contact areabetween the first surface and the second surface when the polypropylenefilm is wound.

Specifically, when the ellipse density D_(A) on the first surface is 50to 120 pieces/mm², it can be said that the number of “ellipses” isrelatively large. Hence, the surface is roughened to a greater degree.Meanwhile, when the ellipse density D_(B) on the second surface is 1 to90 pieces/mm², it can be said that the number of “ellipses” isrelatively small. Hence, the degree of roughening is low although thesurface is roughened.

It is possible to prevent the film from meandering to left and right inthe slitting step processing and the end surfaces of small roll frombeing unmatched if the ellipse density D_(A) on the first surface is setto 50 to 120 pieces/mm² and the ellipse density D_(B) on the secondsurface is set to 1 to 90 pieces/mm² in this manner. As a result, it ispossible to improve the processability in the slitting step as can beseen from Examples as well.

In addition, when the ellipse density D_(A) on the first surface is 50to 120 pieces/mm² and the ellipse density D_(B) on the second surface is1 to 90 pieces/mm², both surfaces of the polypropylene film are moresuitably roughened, and thus the slipperiness with respect to theconveying rolls is more suitable on both surfaces when the polypropylenefilm after being biaxially stretched is wound into a roll. As a result,more suitable conveying property is attained and wrinkling and windingshift are further suppressed.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Generally, when the surface is roughened, thin parts (concave portionsof irregularities) of the film cause leakage current. Hence, it ispossible to diminish the number of irregularities that may cause leakagecurrent if the ellipse density D_(B) on the second surface is set to belower than the ellipse density D_(A) on the first surface. Specifically,it can be said that the number of irregularities that may cause leakagecurrent is small when the ellipse density D_(B) on the second surface is1 to 90 pieces/mm². As a result, a configuration is attained in whichconveying property due to roughening is more suitably exhibited whilethe dielectric strength is more suitably maintained.

The average major axis length LA of the ellipses constituting theellipse density D_(A) on the first surface, the average major axislength L_(B) of the ellipses constituting the ellipse density D_(B) onthe second surface, the ellipse perfectness PA of the ellipsesconstituting the ellipse density D_(A) on the first surface, and theellipse perfectness PB of the ellipses constituting the ellipse densityD_(B) on the second surface are preferably within the numerical rangesdescribed in the section of “embodiment of first present invention”.Moreover, the meanings and determining methods of these parameters havebeen described in the section of “embodiment of first presentinvention”, and thus description thereof is omitted here.

The direct current dielectric breakdown strength ES of the polypropylenefilm at 100° C. and the direct current dielectric breakdown strength ESof the polypropylene film at 120° C. are preferably within the numericalranges described in the section of “embodiment of first presentinvention”.

The ash content in the polypropylene film is preferably within thenumerical range described in the section of “embodiment of first presentinvention”. The method for determining the ash content has beendescribed in the section of “embodiment of first present invention”, andthus description thereof is omitted here.

The thickness of the polypropylene film is preferably within thenumerical range described in the section of “embodiment of first presentinvention”. The method for determining the thickness has been describedin the section of “embodiment of first present invention”, and thusdescription thereof is omitted here.

The polypropylene film may be a biaxially-oriented film, auniaxially-oriented film, or a nonoriented film. Among these, thepolypropylene film is a biaxially-oriented film from the viewpoint ofeasily setting the Spk value (Spk_(A)) of the first surface, the Spkvalue (Spk_(A)) of the first surface, the Svk value (Svk_(B)) of thesecond surface, and the Spk value (Spk_(B)) of the second surface to bewithin the numerical ranges.

The polypropylene film and the metal layer-integrated polypropylene filmare each wound into a roll and preferably in the form of a film roll.The film roll may or may not have a winding core (core). The film rollpreferably has a winding core (core). The material for the winding coreof the film roll is not particularly limited. As the material, thematerials for the winding core described in the section of “embodimentof first present invention” can be adopted.

As described above, the polypropylene film contains a polypropyleneresin as the main component. As the polypropylene resin, thepolypropylene resins described in the section of “embodiment of firstpresent invention” can be adopted.

The polypropylene film may contain resins other than the polypropyleneresins. In addition, the polypropylene film may further contain at leastone kind of additive in addition to the resin components. As the otherresins and additives, the polypropylene resins described in the sectionof “embodiment of first present invention” can be adopted.

The polypropylene film is preferably biaxially stretched. In a case inwhich the polypropylene film is a biaxially-oriented polypropylene film,the biaxially-oriented polypropylene film can be produced by a generallyknown method for producing a biaxially-oriented polypropylene film. Thebiaxially-oriented polypropylene film can be produced, for example, byfabricating a cast sheet from a polypropylene resin composition obtainedby mixing the linear polypropylene resin A, the linear polypropyleneresin B, and the long-chain branched polypropylene resin C with otherresins, additives and the like if necessary and then biaxiallystretching the cast sheet.

<Preparation of Polypropylene Resin Composition>

As the method for preparing the polypropylene resin composition, themethod described in the section of “embodiment of first presentinvention” can be adopted.

<Fabrication of Cast Sheet>

As the method for fabricating the cast sheet, the method described inthe section of “embodiment of first present invention” can be adopted.

<Stretching Treatment>

The biaxially-oriented polypropylene film can be produced by subjectingthe cast sheet to a stretching treatment. As the stretching treatmentmethod, the method described in the section of “embodiment of firstpresent invention” can be adopted.

The polypropylene film may be subjected to a corona discharge treatmentonline or offline after end of the stretching and thermosetting steps.As the corona discharge treatment, the method described in the sectionof “embodiment of first present invention” can be adopted.

In order to process the polypropylene film as a capacitor, a metal layermay be stacked on either surface or both surfaces of the polypropylenefilm to obtain a metal layer-integrated polypropylene film. As thematerial for and the stacking method of the metal layer, the contentsdescribed in the section of “embodiment of first present invention” canbe adopted.

A plurality of the metal layer-integrated polypropylene films can bestacked by a conventionally known method or subjected to an elementwinding processing (winding) to be formed into a film capacitor.

As a specific method for fabricating the film capacitor, the methoddescribed in the section of “embodiment of first present invention” canbe adopted.

Heretofore, the second embodiment (the embodiment according to thesecond present invention) has been described.

Embodiment According to Third Present Invention

Hereinafter, an embodiment of the third present invention will bedescribed. Incidentally, in the polypropylene film according to theembodiment of the third present invention, the Svk value (Svk_(A)) ofthe first surface is not required to be 0.005 μm or more and 0.030 μm orless as in the embodiment of the first present invention. In addition,the Spk value (Spk_(A)) of the first surface is not required to be morethan 0.035 μm and 0.080 μm or less. In addition, the Svk value (Svk_(B))of the second surface is not required to be 0.005 μm or more and 0.030μm or less. In addition, the Spk value (Spk_(B)) of the second surfaceis not required to be 0.015 μm or more and 0.035 μm or less.

In addition, in the polypropylene film according to the embodiment ofthe third present invention, the ratio Spk_(B)/Spk_(A) of the Spk value(Spk_(B)) of the second surface to the Spk value (Spk_(A)) of the firstsurface is not required to be 0.490 or more and 0.730 or less as in theembodiment of the second present invention. In addition, the ratioSvk_(B)/Svk_(A) of the Svk value (Svk_(B)) of the second surface to theSvk value (Svk_(A)) of the first surface is not required to be 0.735 ormore and 1.250 or less.

The polypropylene film according to the embodiment of the third presentinvention (hereinafter, also referred to as “third embodiment”) is apolypropylene film having a first surface and a second surface, in which

-   -   the polypropylene film contains a polypropylene resin as a main        component;    -   an ellipse density D_(A) on the first surface is 85 to 120        pieces/mm²; and    -   an ellipse density D_(B) on the second surface is 1 to 12        pieces/mm².

The ellipse density D_(A) is more preferably 85 to 110 pieces/mm²,further preferably 90 to 105 pieces/mm².

The ellipse density D_(B) is more preferably 3 to 11 pieces/mm², furtherpreferably 4 to 10 pieces/mm².

Both surfaces of the polypropylene film are roughened by crater-likefine irregularities. The crater-like fine irregularities have beendescribed in the section of “embodiment of first present invention”, andthus description thereof is omitted here.

The ellipse density D_(A) on the first surface is 85 to 120 pieces/mm²and the ellipse density D_(B) on the second surface is 1 to 12pieces/mm², thus the contact area between the first surface and thesecond surface when the polypropylene film is wound decreases, the gapbetween the first surface and the second surface can be maintained dueto the difference in ellipse density, and excellent cushioning propertyis exhibited. As a result, it is possible to suppress blocking as can beseen from Examples as well.

In addition, the ellipse density D_(A) on the first surface is 85 to 120pieces/mm² and it can be said that the number of “ellipses” isrelatively large. Hence, the surface is roughened to a greater degree.Meanwhile, the ellipse density D_(B) on the second surface is 1 to 12pieces/mm² and it can be said that the number of “ellipses” isrelatively small. Hence, the degree of roughening is low although thesurface is roughened.

It is possible to prevent the film from meandering to left and right inthe slit processing and the end surfaces of small roll from beingunmatched if the ellipse density D_(A) on the first surface is set to 85to 120 pieces/mm² and the ellipse density D_(B) on the second surface isset to 1 to 12 pieces/mm² in this manner. As a result, it is possible toimprove the processability in the slitting step as can be seen fromExamples as well.

In addition, the polypropylene film is generally wound by using aplurality of conveying rolls while applying tension to the polypropylenefilm in order not to cause wrinkling and meandering. Therefore, not onlyone surface touches the conveying rolls, but the winding is performedwhile both surfaces touch one of the conveying rolls.

According to the polypropylene film, both surfaces of the polypropylenefilm are roughened and thus the slipperiness with respect to theconveying rolls is suitable on both surfaces when the polypropylene filmafter being biaxially stretched is wound into a roll. As a result,suitable conveying property is attained and wrinkling and winding shiftare suppressed.

Specifically, the ellipse density D_(A) on the first surface is 85 to120 pieces/mm² and the ellipse density D_(B) on the second surface is 1to 12 pieces/mm², thus both surfaces of the polypropylene film aresuitably roughened, and thus the slipperiness with respect to theconveying rolls is suitable on both surfaces when the polypropylene filmafter being biaxially stretched is wound into a roll. As a result,suitable conveying property is attained, wrinkling and winding shift arefurther suppressed, and the element winding processability is improved.

Here, it is preferred that the degree of roughening of the first surfaceis about equal to that of the second surface when only the conveyingproperty is taken into consideration. However, it is preferred that thedegree of roughening of the first surface is different from that of thesecond surface when the dielectric strength is taken into consideration.Generally, when the surface is roughened, thin parts (concave portionsof irregularities) of the film cause leakage current. Hence, it ispossible to diminish the number of irregularities that may cause leakagecurrent if the ellipse density D_(B) on the second surface is set to belower than the ellipse density D_(A) on the first surface. Specifically,it can be said that the number of irregularities that may cause leakagecurrent is small when the ellipse density D_(B) on the second surface is1 to 12 pieces/mm². As a result, a configuration is attained in whichmore suitable conveying property due to roughening is exhibited whilethe dielectric strength is suitably maintained.

As described above, according to the polypropylene film according to thethird embodiment, it is possible to suppress blocking and further toachieve all the processability in the slitting step, conveying property,and dielectric strength.

The method for determining the ellipse density has been described in thesection of “embodiment of first present invention”, and thus descriptionthereof is omitted here.

The average major axis length LA of the ellipses constituting theellipse density D_(A) on the first surface, the average major axislength L_(B) of the ellipses constituting the ellipse density D_(B) onthe second surface, the ellipse perfectness PA of the ellipsesconstituting the ellipse density D_(A) on the first surface, and theellipse perfectness PB of the ellipses constituting the ellipse densityD_(B) on the second surface are preferably within the numerical rangesdescribed in the section of “embodiment of first present invention”.Moreover, the meanings and determining methods of these parameters havebeen described in the section of “embodiment of first presentinvention”, and thus description thereof is omitted here.

It is preferred that the ratio Sq_(B)/Sq_(A) of the Sq value (Sq_(B)) ofthe second surface to the Sq value (Sq_(A)) of the first surface, theSq_(A), Sq_(B), the ratio Sa_(B)/Sa_(A) of the Sa value (Sa_(B)) of thesecond surface to the Sa value (Sa_(A)) of the first surface, theSa_(A), the Sa_(B), the ratio Sk_(B)/Sk_(A) of the Sk value (Sk_(B)) ofthe second surface to the Sk value (Sk_(A)) of the first surface, theSk_(A), and the Sk_(B) of the polypropylene film are within thenumerical ranges described in the section of “embodiment of firstpresent invention”. Moreover, the meanings and determining methods ofthese parameters have been described in the section of “embodiment offirst present invention”, and thus description thereof is omitted here.

The method for setting the ellipse density D_(A) on the first surface,the ellipse density D_(B) on the second surface, the average major axislength LA of the ellipses constituting the ellipse density D_(A) on thefirst surface, the average major axis length L_(B) of the ellipsesconstituting the ellipse density D_(B) on the second surface, the Sqvalue (Sq_(A)) of the first surface, the Sq value (Sq_(B)) of the secondsurface, the ratio Sq_(B)/Sq_(A), the Sa value (Sa_(A)) of the firstsurface, the Sa value (Sa_(B)) of the second surface, the ratioSa_(B)/Sa_(A), the Sk value (Sk_(A)) of the first surface, the Sk value(Sk_(B)) of the second surface, and the ratio Sk_(B)/Sk_(A) to be withinthe numerical ranges is not particularly limited, but these values canbe appropriately adjusted by (i) the selection of the kinds,stereoregularity, molecular weight distribution, and differentialdistribution value difference D_(M) of resins (raw material resins)constituting the polypropylene film, (ii) the contents of the respectiveresins with respect to the entire polypropylene film, (iii) the stretchratios in the longitudinal and transverse directions at the time ofstretching and the stretching temperature, (iv) the selection of thekinds of additives (particularly nucleating agent) and the contentsthereof, and the like.

The method for setting the ellipse density D_(A) on the first surfaceand the ellipse density D_(B) on the second surface to be different fromeach other, the method for setting the average major axis length LA ofthe ellipses constituting the ellipse density D_(A) on the first surfaceand the average major axis length L_(B) of the ellipses constituting theellipse density D_(B) on the second surface to be different from eachother, the method for setting the Sq value (Sq_(A)) of the first surfaceand the Sq value (Sq_(B)) of the second surface to be different fromeach other, the method for setting the Sa value (Sa_(A)) of the firstsurface and the Sa value (Sa_(B)) of the second surface to be differentfrom each other, and the method for setting the Sk value (Sk_(A)) of thefirst surface and the Sk value (Sk_(B)) of the second surface to bedifferent from each other are not particularly limited, but these valuescan be adjusted by, for example, fabricating a cast sheet with the firstsurface as the cast roll side surface and the second surface as the airknife side surface and biaxially stretching this cast sheet.

The direct current dielectric breakdown strength ES of the polypropylenefilm at 100° C. and the direct current dielectric breakdown strength ESof the polypropylene film at 120° C. are preferably within the numericalranges described in the section of “embodiment of first presentinvention”.

The ash content in the polypropylene film is preferably within thenumerical range described in the section of “embodiment of first presentinvention”. The method for determining the ash content has beendescribed in the section of “embodiment of first present invention”, andthus description thereof is omitted here.

The thickness of the polypropylene film is preferably within thenumerical range described in the section of “embodiment of first presentinvention”. The method for determining the thickness has been describedin the section of “embodiment of first present invention”, and thusdescription thereof is omitted here.

The polypropylene film may be a biaxially-oriented film, auniaxially-oriented film, or a nonoriented film. Among these, thepolypropylene film is preferably a biaxially-oriented film from theviewpoint of easily setting the ellipse density D_(A) and the ellipsedensity D_(B) to be within the numerical ranges.

The polypropylene film and the metal layer-integrated polypropylene filmare each wound into a roll and preferably in the form of a film roll.The film roll may or may not have a winding core (core). The film rollpreferably has a winding core (core). The material for the winding coreof the film roll is not particularly limited. As the material, thematerials for the winding core described in the section of “embodimentof first present invention” can be adopted.

As described above, the polypropylene film contains a polypropyleneresin as the main component. As the polypropylene resin, thepolypropylene resins described in the section of “embodiment of firstpresent invention” can be adopted.

The polypropylene film may contain resins other than the polypropyleneresins. In addition, the polypropylene film may further contain at leastone kind of additive in addition to the resin components. As the otherresins and additives, the polypropylene resins described in the sectionof “embodiment of first present invention” can be adopted.

The polypropylene film is preferably biaxially stretched. In a case inwhich the polypropylene film is a biaxially-oriented polypropylene film,the biaxially-oriented polypropylene film can be produced by a generallyknown method for producing a biaxially-oriented polypropylene film. Thebiaxially-oriented polypropylene film can be produced, for example, byfabricating a cast sheet from a polypropylene resin composition obtainedby mixing the linear polypropylene resin A, the linear polypropyleneresin B, and the long-chain branched polypropylene resin C with otherresins, additives and the like if necessary and then biaxiallystretching the cast sheet.

<Preparation of Polypropylene Resin Composition>

As the method for preparing the polypropylene resin composition, themethod described in the section of “embodiment of first presentinvention” can be adopted.

<Fabrication of Cast Sheet>

As the method for fabricating the cast sheet, the method described inthe section of “embodiment of first present invention” can be adopted.

<Stretching Treatment>

The biaxially-oriented polypropylene film can be produced by subjectingthe cast sheet to a stretching treatment. As the stretching treatmentmethod, the method described in the section of “embodiment of firstpresent invention” can be adopted.

The polypropylene film may be subjected to a corona discharge treatmentonline or offline after end of the stretching and thermosetting steps.As the corona discharge treatment, the method described in the sectionof “embodiment of first present invention” can be adopted.

In order to process the polypropylene film as a capacitor, a metal layermay be stacked on either surface or both surfaces of the polypropylenefilm to obtain a metal layer-integrated polypropylene film. As thematerial for and the stacking method of the metal layer, the contentsdescribed in the section of “embodiment of first present invention” canbe adopted.

A plurality of the metal layer-integrated polypropylene films can bestacked by a conventionally known method or subjected to an elementwinding processing (winding) to be formed into a film capacitor.

Specifically, a blade is placed in the center of each margin portion ofthe metal layer-integrated polypropylene film and slit processing isperformed to fabricate a take-up reel having a margin on one surfacethereof.

Here, in the polypropylene film, the ellipse density D_(A) and theellipse density D_(B) are within predetermined numerical ranges and thusblocking is suppressed. Hence, it is possible to prevent thepolypropylene film from blocking and wrinkling in the machine directionof the film from occurring at the time of the slitting processing.

Next, two sheets of a take-up reel with a left margin and a take-up reelwith a right margin are superposed and wound in the width direction sothat the vapor deposition part protrudes more than the margin portion(element winding processing). Next, the core material is removed fromthe wound body and the wound body is pressed. Next, external electrodesare formed on both end surfaces, and further the external electrodes areprovided with lead wires. In this manner, a wound film capacitor isobtained.

Heretofore, the embodiment according to the third present invention hasbeen described.

EXAMPLES

Hereinafter, the present invention (first present invention, secondpresent invention, and third present invention) will be described indetail with reference to Examples, but the present invention (firstpresent invention, second present invention, and third presentinvention) is not limited to the following Examples as long as the gistis not exceeded.

Examples According to First Present Invention

Hereinafter, Examples according to the first present invention will befirst described.

[Polypropylene Resin]

Table 1 shows polypropylene resins used to produce polypropylene filmsof Examples and Comparative Examples.

Resin A1 shown in Table 1 is a product available from Prime Polymer Co.,Ltd. Resin A2 is a product available from Prime Polymer Co., Ltd. ResinB1 is S802M available from KOREA PETRO CHEMICAL IND CO., LTD. Resin B2is HPT-1 available from KOREA PETRO CHEMICAL IND CO., LTD. Resin B3 isavailable from KOREA PETRO CHEMICAL IND CO., LTD. Resin C1 is MFX6available from JAPAN POLYPROPYLENE CORPORATION. Resin X1 is WB135HMS(Daploy HMS-PP) available from Borealis. Incidentally, MFX6 is along-chain branched polypropylene resin polymerized using a metallocenecatalyst. WB135HMS is a long-chain branched polypropylene resin obtainedthrough crosslinking modification by a peroxide. Resin A1 and Resin A2correspond to the linear polypropylene resin A. Resin B1, Resin B2, andResin B3 correspond to the linear polypropylene resin B. Resin C1corresponds to the long-chain branched polypropylene resin C. Resin A1,Resin A2, Resin B1, Resin B2, and Resin B3 are all homopolypropyleneresins. Resin X2 is a product available from Prime Polymer Co., Ltd. andis linear homopolypropylene.

Table 1 shows the number average molecular weight (Mn), weight averagemolecular weight (Mw), z average molecular weight (Mz), molecular weightdistribution (Mw/Mn), and molecular weight distribution (Mz/Mn) of eachresin. These values are values attained when the resins are in the formof raw material resin pellets. The measuring methods are as follows.

<Measurement of Number Average Molecular Weight (Mn), Weight AverageMolecular Weight (Mw), z Average Molecular Weight (Mz), Molecular WeightDistribution (Mw/Mn), and Molecular Weight Distribution (Mz/Mn) ofLinear Polypropylene Resin>

The weight average molecular weight (Mw), number average molecularweight (Mn), z average molecular weight (Mz), molecular weightdistribution (Mw/Mn), and molecular weight distribution (Mz/Mn) of eachresin were measured by GPC (gel permeation chromatography) under thefollowing conditions.

Specifically, a differential refractometer (RI)-incorporated hightemperature GPC apparatus, model HLC-8121GPC-HT available from TOSOHCORPORATION was used. As the column, three TSKgel GMHHR-H(20)HTavailable from TOSOH CORPORATION were connected and used. Themeasurement was performed by setting the column temperature to 140° C.and allowing trichlorobenzene as an eluent to flow at a flow rate of 1.0ml/min. A calibration curve regarding molecular weight M was createdusing standard polystyrene available from TOSOH CORPORATION, andmeasured values were converted into the molecular weight ofpolypropylene using the Q-factor to attain the weight average molecularweight (Mw), number average molecular weight (Mn), and z averagemolecular weight (Mz). The molecular weight distribution (Mw/Mn) wasattained using these values of Mw and Mn. In addition, the molecularweight distribution (Mz/Mn) was attained using these values of Mz andMn.

<Measurement of Number Average Molecular Weight (Mn), Weight AverageMolecular Weight (Mw), z Average Molecular Weight (Mz), Molecular WeightDistribution (Mw/Mn), and Molecular Weight Distribution (Mz/Mn) ofLong-Chain Branched Polypropylene>

The number average molecular weight (Mn), weight average molecularweight (Mw), z average molecular weight (Mz), molecular weightdistribution (Mw/Mn), and molecular weight distribution (Mz/Mn) ofpolypropylene were measured by GPC (gel permeation chromatography) underthe following conditions.

A differential refractometer (RI)-incorporated high temperature GPCapparatus, model HLC-8121GPC-HT available from TOSOH CORPORATION wasused. As the column, three TSKgel GMHHR-H(20)HT available from TOSOHCORPORATION were connected and one TSKgel guard column HHR (30) wasfurther used. The measurement was performed by setting the columntemperature to 140° C. and allowing 0.05 wt %2,6-di-tert-butyl-para-cresol (general name: BHT) in1,2,4-trichlorobenzene as an eluent to flow at a flow rate of 1.0ml/min, and the weight average molecular weight (Mw), number averagemolecular weight (Mn), and z average molecular weight (Mz) wereattained. The molecular weight distribution (Mz/Mn) was attained usingthese values of Mz and Mn, and the molecular weight distribution (Mw/Mn)was attained using these values of Mw and Mn. The measurement conditionsare as follows.

-   -   GPC apparatus: HLC-8121GPC/HT (available from TOSOH CORPORATION)    -   Light scattering detector: DAWN EOS (Wyatt Technology        Corporation),    -   Column: TSKgel guard column HHR (30) (7.8 mm ID×7.5        cm)×1+TSKgelGMH-HR-H(20)HT (7.8 mm ID×30 cm)×3 (available from        TOSOH CORPORATION)    -   Eluent: 0.05 wt % BHT in 1,2,4-trichlorobenzene    -   Flow rate: 1.0 ml/min    -   Sample concentration: 2 mg/mL    -   Injection volume: 300 μL    -   Column temperature: 140° C.    -   System temperature: 40° C.    -   Pretreatment: The sample was precisely weighed, added to the        eluent, shaken and dissolved at 140° C. for 1 hour, and        heat-filtered through a 0.5 μm sintered metal filter.        <Measurement of Differential Distribution Value when Logarithmic        Molecular Weight Log (M)=4.5, Differential Distribution Value        when Logarithmic Molecular Weight Log (M)=6.0, and Differential        Distribution Value Difference D_(M)>

For each resin, the differential distribution value when the logarithmicmolecular weight log (M)=4.5 and the differential distribution valuewhen the logarithmic molecular weight log (M)=6.0 were attained by thefollowing methods. First, the time curve (elution curve) of theintensity distribution detected by using the RI detector was convertedinto a distribution curve with respect to the molecular weight M (Log(M)) of standard polystyrene using the calibration curve created usingthe standard polystyrene. Next, the integral distribution curve withrespect to Log (M) when the total area of the distribution curve was100% was attained, and then this integral distribution curve wasdifferentiated by Log (M) to attain the differential distribution curvewith respect to Log (M). From this differential distribution curve, thedifferential distribution values at Log (M)=4.5 and Log (M)=6.0 wereread out. In addition, the difference between the differentialdistribution value when Log (M)=4.5 and the differential distributionvalue when Log (M)=6.0 was defined as the differential distributionvalue difference D_(M). Incidentally, the series of operations until thedifferential distribution curve was attained was performed usinganalytical software incorporated in the GPC measuring apparatus used.The results are shown in Table 1.

<Measurement of Melt Flow Rate (MFR)>

For each resin, the melt flow rate (MFR) in the form of raw materialresin pellets was measured in accordance with the condition M of JIS K7210 using a melt indexer available from TOYO SEIKI Co., Ltd.Specifically, 4 g of sample was first inserted into a cylinder set to atest temperature of 230° C. and preheated for 3.5 minutes under a loadof 2.16 kg. Thereafter, the weight of the sample extruded through thebottom hole for 30 seconds was measured, and MFR (g/10 min) wasdetermined. The measurement was repeated three times, and the averagevalue thereof was taken as the measured value of MFR. The results areshown in Table 1.

<Measurement of Heptane Insoluble (HI)>

Each resin was press-molded into a size of 10 mm×35 mm×0.3 mm and asample for measurement of about 3 g was fabricated. Next, about 150 mLof heptane was added thereto and Soxhlet extraction was performed for 8hours. The heptane insolubles were calculated from the sample massesbefore and after the extraction. The results are shown in Table 1.

<Measurement of Ash Content>

The ash content in each resin was measured as follows.

A sample was weighed by about 200 g, transferred to a platinum dish, andasked at 800° C. for 40 minutes. The ash content (ppm) was measured fromthe obtained ash residue. The results are shown in Table 1.

<Mesopentad Fraction>

Each resin was dissolved in a solvent and subjected to the measurementunder the following conditions using a high temperature type Fouriertransformation nuclear magnetic resonance apparatus (high temperatureFT-NMR).

-   -   High temperature type nuclear magnetic resonance (NMR)        apparatus: high temperature type Fourier transformation nuclear        magnetic resonance apparatus (high temperature FT-NMR),        JNM-ECP500 available from JEOL Ltd.    -   Observation nucleus: 13C (125 MHz)    -   Measurement temperature: 135° C.    -   Solvent: ortho-dichlorobenzene (ODCB: mixed solvent (mixing        ratio=4/1) of ODCB and deuterated ODCB)    -   Measurement mode: single pulse proton broadband decoupling    -   Pulse width: 9.1 μsec (45° pulse)    -   Pulse interval: 5.5 sec    -   Number of times of integration: 4,500    -   Shift basis: CH3 (mmmm)=21.7 ppm

The pentad fraction indicating the stereoregularity was calculated inpercentage (%) based on the integrated value of the intensity of eachsignal derived from the combination (mmmm, mrrm and the like) of pentadof isotactic diad “meso (m)” and syndiotactic diad “racemo (r)”.Regarding attribution of each signal derived from mmmm, mrrm and thelike, for example, description of spectrum in “T. Hayashi et al.,Polymer, vol. 29, p. 138 (1988)” and so on were referenced.

TABLE 1 Resin Resin Resin Resin Resin Resin Resin Resin Resin A1 A2 B1B2 B3 C1 X1 X2 Nμmber average molecular weight 33 34 46 45 44 160 180 47(M_(n)) × 10³ Weight average molecular weight 310 340 380 350 350 380540 270 (M_(w)) × 10³ z average molecular weight (M_(z)) × 10³ 1400 15001600 1600 1500 840 1500 750 Molecular weight M_(w)/M_(n) 9.4 10.0 8.37.8 8.0 2.4 3.0 5.7 distribution M_(z)/M_(n) 42.4 45.5 34.8 35.6 34.85.3 8.3 16.0 Differential log(M) = 4.5 33.5 33.7 27.3 31.3 32.7 — — 29.9distribution value log(M) = 6.0 24.5 23.5 30.9 27.7 25.7 — — 21.4Differential distribution value difference 9.0 10.2 −3.6 3.6 7.0 — — 8.6[%] MFR [g/10 min] 4.9 4.9 2.3 3.8 3.8 2.0 2.4 5.6 Heptane insolubles(HI) [%] 97.3 97.3 98.8 98.6 98.6 98.9 97.9 97.8 Ash content [ppm] 2 ×10 2 × 10 3 × 10 3 × 10 3 × 10 35 × 10 55 × 10 2 × 10 Mesopentadfraction [mmmm] [%] 95.8 95.1 98.0 97.2 96.5 — — 97.4

Polypropylene films of Examples and Comparative Examples were producedusing the resins described above and the physical properties thereofwere evaluated.

Fabrication of Polypropylene Film Example 1

Resin A1, Resin B1, and Resin C1 were dry-blended. The mixing ratio wasset to (Resin A1):(Resin B1):(Resin C1)=63:34:3 in terms of mass ratio.After that, the dry-blended resin was melted at a resin temperature of250° C., then extruded using a T die, wound around a metal drum of whichthe surface temperature was kept at 95° C., and solidified to fabricatea cast sheet. At this time, the cast sheet was fabricated while pressingthe melt-extruded resin composition against the metal drum with an airknife. The unstretched cast sheet obtained was kept at a temperature of130° C., and allowed to pass between rolls running at different speedsto be stretched to 4.5 times in the machine direction, and immediatelycooled to room temperature. Subsequently, the stretched sheet was guidedto the tenter, and stretched to 8 times in the width direction at atemperature of 158° C., and then subjected to relaxation andthermosetting, and wound, and subjected to an aging treatment in anatmosphere at about 40° C. to obtain a polypropylene film according toExample 1.

Examples 2 to 5 and Comparative Examples 1 to 6

Polypropylene films according to Examples 2 to 5 and ComparativeExamples 1 to 6 were obtained in the same manner as in Example 1 exceptthat the mixing ratio at the time of dry blending of the raw materialresins was changed as shown in Table 2.

However, in Comparative Example 6, it was not be able to fabricate asmooth cast sheet because of melt fracture at the time of extrusionmolding. For this reason, breakage occurred when the cast sheet wasstretched.

Examples 6 to 8, Comparative Example 7, and Comparative Example 8

Polypropylene films according to Examples 6 to 8, Comparative Example 7,and Comparative Example 8 were obtained in the same manner as in Example1 except that the mixing ratio at the time of dry blending of the rawmaterial resins was changed as shown in Table 2.

TABLE 2 Comparative Example Example Example Example Example ExampleExample Example Example 1 2 3 4 5 6 7 8 1 Resin A1 63 63 63 62 64 60 6098 65 (parts by mass) Resin A2 — — — — — — — — — (parts by mass) ResinB1 34 34 — 33 — — 30 — — (parts by mass) Resin B2 — — 34 — 35 30 — — 35(parts by mass) Resin B3 — — — — — — — — — (parts by mass) Resin C1  3 3  3  5  1 10 10  2 — (parts by mass) Resin X1 — — — — — — — — — (partsby mass) Resin X2 — — — — — — — — — (parts by mass) ComparativeComparative Comparative Comparative Comparative Comparative ComparativeExample Example Example Example Example Example Example 2 3 4 5 6 7 8Resin A1 65 63 100 — — — 98 (parts by mass) Resin A2 — — — 64 — — —(parts by mass) Resin B1 35 34 — — — — — (parts by mass) Resin B2 — — —— — — — (parts by mass) Resin B3 — — — 34 — — — (parts by mass) Resin C1— — — — 100  2 — (parts by mass) Resin X1 —  3 —  2 — —  2 (parts bymass) Resin X2 — — — — — 98 — (parts by mass)

<Measurement of Thickness of Polypropylene Film>

The thickness of the polypropylene films of Examples and ComparativeExamples was measured. Specifically, the thickness was measured inaccordance with JIS-C2330 except that the measurement was performed at100±10 kPa using a paper thickness measuring device MEI-11 availablefrom Citizen Seimitsu Co., Ltd. The results are shown in Table 3.

<Measurement of Svk value (Svk_(A)) of first surface, Spk value(Spk_(A)) of first surface, Svk value (Svk_(B)) of second surface, Spkvalue (Spk_(B)) of second surface, Sq value (Sq_(A)) of first surface,Sq value (Sq_(B)) of second surface, Sa value (Sa_(A)) of first surface,Sa value (Sa_(B)) of second surface, Sk value (Sk_(A)) of first surface,and Sk value (Sk_(B)) of second surface>

Hereinafter, the first surface is referred to as “surface A” and thesecond surface is referred to as “surface B” in some cases. In Table 3as well, the terms surface A and surface B are used in some cases.

As an optical interference type non-contact surface shape measuringinstrument, “VertScan 2.0 (model: R5500GML)” available from RyokaSystems, Inc. was used.

First, the measurement was performed in a region of 470.92 μm×353.16 μmper one visual field at the WAVE mode by applying a 530 white filter anda 1× BODY lens tube and using an objective lens (10×). This operationwas performed at 10 positions at 1 cm intervals in the machine directionfrom the position to be the center in both the machine direction andwidth direction of the target sample (polypropylene film).

Next, the acquired data was subjected to noise removal processing by amedian filter (3×3) and then to Gaussian filter processing at a cutoffvalue of 30 μm to remove the waviness component. By this, a state wasattained in which the state of the roughened surface was able to beproperly measured.

Next, analysis was performed using the “ISO parameter” in the plug-infunction “Bearing” of the analysis software “VS-Viewer” of “VertScan2.0”.

Finally, the average values were each calculated for the respectivevalues (Svk_(A), Spk_(A), Svk_(B), Spk_(B), Sq_(A), Sq_(B), Sa_(A),Sa_(B), Sk_(A), and Sk_(B)) attained at the 10 positions. The Svk value(Svk_(A)) of the first surface, the Spk value (Spk_(A)) of the firstsurface, the Svk value (Svk_(B)) of the second surface, the Spk value(Spk_(B)) of the second surface, the Sq value (Sq_(A)) of the firstsurface, the Sq value (Sq_(B)) of the second surface, the Sa value(Sa_(A)) of the first surface, the Sa value (Sa_(B)) of the secondsurface, the Sk value (Sk_(A)) of the first surface, and the Sk value(Sk_(B)) of the second surface were determined in this manner. Theresults are shown in Table 3. Incidentally, Table 3 also shows thevalues of the ratio Sq_(B)/Sq_(A), the ratio Sa_(B)/Sa_(A), and theratio Sk_(B)/Sk_(A).

<Measurement of Ellipse Density>

The ellipse densities of the first surface (surface A) and the secondsurface (surface B) of the polypropylene films of Examples andComparative Examples were measured. Specifically, each surface of thepolypropylene film was observed at a lens magnification: 100-fold, by ameasurement method: reflection measurement, in a visual field range: 3.4mm×2.6 mm using a digital scope (Digital Microscope VHX-2000 availablefrom Keyence Corporation), and the number of “ellipses” observed in thevisual field range was counted. Thereafter, the number was convertedinto the number per unit area. The results are shown in Table 3.

Incidentally, those satisfying S≤L and 1≤L≤300, where the length of oneaxis was denoted as L μm and the length of the other axis was denoted asS μm, were defined as “ellipses” to be considered when the ellipsedensity was calculated. Those that did not satisfy this were notconsidered when the ellipse density was calculated (not counted as“ellipses” when the ellipse density was calculated).

<Measurement of Average Major Axis Length>

The average value of the major axes of the ellipses observed in themeasurement of ellipse density was calculated. The results are shown inTable 3.

<Measurement of Ellipse Perfectness>

First, surface shape data in a region of 470.92 μm×353.16 μm per onevisual field was acquired at the WAVE mode by applying a 530 whitefilter and a 1× BODY lens tube and using an objective lens (10×) and“VertScan 2.0 (model: R5500GML)” available from Ryoka Systems, Inc. asan optical interference type non-contact surface shape measuringinstrument. This operation was performed at 10 positions at 1 cmintervals in the machine direction from the position to be the center inboth the machine direction and width direction of the target sample(polypropylene film).

Next, the acquired data was subjected to noise removal processing by amedian filter (3×3) and then to Gaussian filter processing at a cutoffvalue of 30 μm to remove the waviness component.

Three crater projection images each consisting of paired arcs wereextracted from each of the projection images of surface shape data at 10positions acquired as described above. Incidentally, the projectionimage was defined as a projection image acquired by projecting partshaving a height of 0.02 μm or more among fine irregularities onto thefilm surface.

When extracting crater projection images, three crater projection imagesin which arcs based on different β-spherulites were not acknowledged tooverlap each other were extracted. As the method for extracting threecrater projection images, the ellipses which became the quartiles (firstquartile, second quartile (namely, median value), and third quartile) inthe area of ellipse by visual observation were extracted.

Next, for each of the three extracted crater projection images, thetotal length Lt of the paired arcs and the total circumferential lengthLc of the virtual circular ring including the paired arcs were measuredto determine the ratio (Lt/Lc). Thereafter, the values of the ratio fortotal 30 images thus attained were averaged to attain the average valuea of the ratio (Lt/Lc).

The determination of virtual circular ring and the measurement of Lt andLc were performed using the plug-in function “edge curve length” of theanalysis software “VS-Viewer” of the optical interference typenon-contact surface shape measuring instrument VertScan 2.0. Thespecific procedure is as follows.

(1) First, two points farthest from each other on arcs 30 a and 30 b aredenoted as P₁ and P₂ and a straight line (hereinafter, referred to asstraight line (P₁-P₂)) connecting P₁ and P₂ is determined as illustratedin FIG. 3A.

(2) Subsequently, an ellipse (E₀) is derived from the shape (locationdata) of the arcs 30 a and 30 b at the part located on one side (theupper side of the straight line (P₁-P₂) in FIG. 3A) of the straight line(P₁-P₂) by the least-squares method so that the straight line (P₁-P₂)becomes the major axis as illustrated in FIG. 3B. Thereafter, the curve(a part of the circumference of the ellipse (E₀)) constituting thisellipse (E₀) complements the part between the arcs 30 a and 30 b on theone side to form a complementary line 40 a. Incidentally, the ellipse(E₀) is not illustrated except for the part corresponding to thecomplementary line 40 a in FIG. 3B.

(3) Subsequently, an ellipse (E₁) is derived from the shape (locationdata) of the arcs 30 a and 30 b at the part located on the other side(the lower side of the straight line (P₁-P₂) in FIG. 3A) of the straightline (P₁-P₂) by the least-squares method so that the straight line(P₁-P₂) becomes the major axis as illustrated in FIG. 3C. Thereafter,the curve (a part of the circumference of the ellipse (E₁)) constitutingthis ellipse (E₁) complements the part between the arcs 30 a and 30 b onthe other side to form a complementary line 40 b. Incidentally, theellipse (E₁) is not illustrated except for the part corresponding to thecomplementary line 40 b in FIG. 3C.

(4) The circular ring which is connected by the complementary lines 40 aand 40 b thus determined and the arcs 30 a and 30 b and illustrated inFIG. 3C is a virtual circular ring.

(5) Thereafter, a height profile of fine irregularities 20 is drawnwhich indicates the heights of the fine irregularities 20 at therespective locations with respect to the respective locations (distanceswhen a point on the circumference is used as the basis) on thecircumference of this virtual circular ring. Lt and Lc in a craterprojection image G corresponding to the part having a height of 0.02 μmor more are read out from this height profile.

Incidentally, 30 pieces (n=30) of location data are used for each whenthe least-squares method is carried out.

<Measurement of Dielectric Breakdown Strength of Polypropylene Film(Dielectric Strength Evaluation)>

The dielectric breakdown voltage value of the polypropylene film wasmeasured 12 times at 100° C. and 125° C. using a DC power source inaccordance with JIS C2330 (2001) 7.4.11.2 Method B (plate electrodemethod). The dielectric breakdown voltage value V_(DC) was divided bythe film thickness (μm), and the average value for 8 points excludingthe upper 2 points and the lower 2 points among the measurement resultsfor 12 times was defined as the dielectric breakdown strength ES(V_(DC)/μm). The results are shown in Table 3.

Incidentally, in Comparative Examples 1 and 4, it can be seen that thedielectric breakdown strength at 120° C. is less than 485 V_(DC)/μm andthe dielectric strength is poor.

<Evaluation on Blocking of Metal Vapor-Deposited Roll>

A metal layer-integrated polypropylene film was obtained by subjecting abiaxially-oriented polypropylene film to aluminum vapor deposition at avapor deposition resistance of 15Ω/□ to form a T-margin vapor depositionpattern. The pattern vapor deposition was performed according to avacuum vapor deposition method by a wire system, and the heavy edgevapor deposition was performed according to a vacuum vapor depositionmethod by a crucible system. The film used for vapor deposition had awidth of 620 mm, and the film length after vapor deposition was 50,000m. A blade was placed in the center of each margin of this 620 mm widemetal layer-integrated polypropylene film, and slit processing wasperformed at a slit speed of 350 m/min so as to obtain small rolls witha width of 30 mm and a length of 10,000 m. At that time, it wasevaluated as AA in a case in which wrinkles in the machine directiongenerated by blocking of the vapor-deposited surface and thenon-vapor-deposited surface were not observed at the metal vapordeposition winding and unwinding parts, A in a case in which slightstreaks which were not wrinkles were observed, B in a case in whichwrinkles in the machine direction were observed at the end portion inthe width direction, and C in a case in which wrinkles in the machinedirection were observed even at the central portion in the widthdirection. The results are shown in Table 3.

<Measurement of Ash Content>

The ash content in the polypropylene films of Examples and ComparativeExamples was measured as follows.

A sample was weighed by about 200 g, transferred to a platinum dish, andasked at 800° C. for 40 minutes. The ash content (ppm) was measured fromthe obtained ash residue. The results are shown in Table 3.

<Evaluation on Processability in Slitting Step>

A metal vapor-deposited roll having a width of 620 mm was slit at a slitspeed of 350 m/min so as to have a width of 30 mm and a length of 10,000m and was thus divided into 20 pieces in the width direction. As aresult, it was evaluated as A in a case in which the end surface shift(the shift length when the film meandered left and right at the time ofwinding and the end surfaces of small roll were unmatched) in all the 20small rolls obtained was within 0.5% of the slit width, B in a case inwhich the end surface shift in all the 20 small rolls was within 1.0% ofthe slit width and did not reach the evaluation A, C in a case in whichthe end surface shift in all the 20 small rolls was within 2.0% of theslit width and did not reach the evaluation B, and D in a case in whichthe end surface shift was more than 2.0% of the slit width in one ormore of the 20 small rolls. The results are shown in Table 3.

<Evaluation on Element Winding Processability>

Among the small rolls obtained in the evaluation on slit processability,two sheets of a take-up reel with a left margin and a take-up reel witha right margin were superposed and wound in the width direction so thatthe vapor deposition part protruded more than the margin portion(element winding processing). The winding was performed by 1360 turns ata winding tension of 200 g using an automated winder 3KAW-N2 availablefrom KAIDO MFG. CO., LTD. At that time, the rolls were visually observedfrom the beginning of winding to the end of winding, and those in whichwrinkling and shift occurred were judged to be unacceptable, and theproportion of the number of unacceptable products to the total number ofproduced products was expressed as a percentage and used as an index ofprocessability (hereinafter referred to as element winding yield). It ismore preferable as the element winding yield is higher. An elementwinding yield of 95% or more was evaluated to be favorable “◯”, and anelement winding yield of less than 95% was evaluated to be defective“x”. The results are shown in Table 3.

TABLE 3 Com- Com- Com- Com- Com- Com- Com- Com- parative parativeparative parative parative parative parative parative Example ExampleExample Example Example Example Example Example Example Example ExampleExample Example Example Example Example 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8Thickness [μm] 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 — 2.32.3 Spk [μm] Spk_(A) (Spk of 0.048 0.080 0.049 0.043 0.060 0.040 0.0350.080 0.082 0.079 0.051 0.086 0.050 — 0.073 0.041 surface A) Spk_(B)(Spk of 0.024 0.022 0.032 0.021 0.034 0.027 0.024 0.026 0.038 0.0280.014 0.040 0.014 — 0.028 0.009 surface B) Svk [μm] Svk_(A) (Svk of0.011 0.030 0.013 0.010 0.022 0.029 0.025 0.028 0.039 0.033 0.012 0.0410.012 — 0.032 0.029 surface A) Svk_(B) (Svk of 0.010 0.011 0.016 0.0090.015 0.025 0.022 0.022 0.014 0.009 0.009 0.014 0.010 — 0.026 0.009surface B) Sq [μm] Sq_(A) (Sq of 0.028 0.069 0.032 0.025 0.049 0.0510.045 0.067 0.081 0.071 0.038 0.089 0.040 — 0.066 0.050 surface A)Sq_(B) (Sq of 0.014 0.015 0.023 0.013 0.025 0.042 0.037 0.038 0.0280.017 0.010 0.031 0.011 — 0.043 0.015 surface B) Sq_(B)/Sq_(A) 0.5000.217 0.719 0.520 0.510 0.827 0.827 0.563 0.346 0.239 0.263 0.348 0.275— 0.659 0.297 Sa [μm] Sa_(A) (Sa of 0.014 0.021 0.017 0.012 0.018 0.0170.015 0.020 0.019 0.016 0.014 0.020 0.014 — 0.020 0.017 surface A)Sa_(B) (Sa of 0.010 0.011 0.014 0.009 0.012 0.014 0.013 0.013 0.0110.008 0.008 0.012 0.09 — 0.015 0.005 surface B) Sa_(B)/Sa_(A) 0.7140.524 0.824 0.750 0.667 0.840 0.834 0.655 0.579 0.500 0.571 0.600 0.600— 0.726 0.306 Sk [μm] Sk_(A) (Sk of 0.040 0.057 0.046 0.036 0.045 0.0500.046 0.052 0.043 0.038 0.040 0.045 0.039 — 0.056 0.048 surface A)Sk_(B) (Sk of 0.031 0.032 0.039 0.028 0.036 0.043 0.038 0.039 0.0310.024 0.023 0.032 0.024 — 0.044 0.015 surface B) Sk_(B)/Sk_(A) 0.7750.561 0.848 0.778 0.800 0.855 0.839 0.738 0.721 0.632 0.575 0.711 0.615— 0.790 0.316 Ellipse D_(A) (ellipse 94 93 86 103 84 119 117 86 74 81 8075 81 — 83 80 density density on [pieces/ surface A) mm²] D_(B) (ellipse6 5 11 6 12 7 6 12 14 6 0 13 0 — 11 0 density on surface B) D_(B)/D_(A)0.0638 0.0538 0.1279 0.0583 0.1429 0.0588 0.0513 0.1395 0.1892 0.07410.0000 0.1733 0.0000 — 0.1325 0.0000 Average L_(A) (average 51 59 56 4567 39 41 89 89 80 70 90 70 — 52 73 major axis major axis length lengthon [μm] surface A) L_(B) (average 57 67 54 52 73 43 47 110 111 118 — 110— — 60 — major axis length on surface B) L_(B)/L_(A) 1.118 1.136 0.9641.156 1.090 1.103 1.146 1.236 1.247 1.475 — 1.222 — — 1.154 — EllipseP_(A) (ellipse 43 57 49 43 50 60 63 50 51 45 39 51 40 — 44 43perfectness perfectness [%] on surface A) P_(B) (ellipse 27 32 32 27 3337 41 31 35 30 13 36 14 — 29 — perfectness on surface B) P_(B)/P_(A)0.628 0.561 0.653 0.628 0.660 0.617 0.651 0.620 0.686 0.667 0.333 0.7060.350 — 0.659 — Dielectric [V_(DC)/μm] 543 510 530 537 528 555 561 534528 542 532 504 530 — 531 520 breakdown strength at 100° C. Dielectric[V_(DC)/μm] 515 490 500 512 501 505 506 490 482 505 486 462 485 — 480475 breakdown strength at 120° C. Ash content [ppm] 3 × 10 3 × 10 3 × 104 × 10 2 × 10 5 × 10 5 × 10 3 × 10 2 × 10 2 × 10 4 × 10 2 × 10 3 × 10 35× 10 2 × 10 3 × 10 Evaluation on blocking AA AA AA AA AA AA AA AA A C CA C — A C suppressing property of metal vapor-deposited roll Evaluationon A A A A B A A A C D C C C — C C processability in slitting stepEvaluation on element ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ — ○ ○ windingprocessability

<Fabrication of Capacitor and Capacitance>

Capacitors were fabricated as follows using the polypropylene filmsobtained in Examples. A metal layer-integrated polypropylene filmincluding a metal film on either surface of the polypropylene film wasobtained by subjecting the polypropylene film to aluminum vapordeposition at a vapor deposition resistance of 15Ω/□ to form a T-marginvapor deposition pattern. After the film was slit into a width of 60 mm,two metal layer-integrated polypropylene films were combined and woundby 1076 turns at a winding tension of 250 g using an automated winder3KAW-N2 available from KAIDO MFG. CO., LTD. The wound element wassubjected to a heat treatment at 120° C. for 15 hours under pressing,and then zinc metal was thermally sprayed on the element end surface toobtain a flat-shaped capacitor. A lead wire was soldered to the endsurface of the flat-shaped capacitor, and the flat-shaped capacitor wasthen sealed with epoxy resin. The capacitances of the finishedcapacitors were all 75 μF (±5 μF).

Heretofore, Examples according to the first present invention has beendescribed.

Examples According to Second Present Invention

Next, Examples according to the second present invention will bedescribed.

Polypropylene films of the following Examples and Comparative Exampleswere fabricated using the polypropylene resins (Resin A1, Resin A2,Resin B1, Resin B2, Resin C1, Resin X1, and Resin X2) described in thesection of “Examples according to first present invention”, and thephysical properties thereof were evaluated.

Fabrication of Polypropylene Film Example 9

Resin A1, Resin B1, and Resin C1 were dry-blended. The mixing ratio wasset to (Resin A1):(Resin B1):(Resin C1)=64:33:3 in terms of mass ratio.After that, the dry-blended resin was melted at a resin temperature of250° C., then extruded using a T die, wound around a metal drum of whichthe surface temperature was kept at 95° C., and solidified to fabricatea cast sheet. At this time, the cast sheet was fabricated while pressingthe melt-extruded resin composition against the metal drum with an airknife. The unstretched cast sheet obtained was kept at a temperature of130° C., and allowed to pass between rolls running at different speedsto be stretched to 4.5 times in the machine direction, and immediatelycooled to room temperature. Subsequently, the stretched sheet was guidedto the tenter, and stretched to 8 times in the width direction at atemperature of 158° C., and then subjected to relaxation andthermosetting, and wound, and subjected to an aging treatment in anatmosphere at about 40° C. to obtain a polypropylene film according toExample 9.

Example 10 and Comparative Examples 9 to 14

Polypropylene films according to Example 10 and Comparative Examples 9to 14 were obtained in the same manner as in Example 9 except that themixing ratio at the time of dry blending of the raw material resins waschanged as shown in Table 4.

However, in Comparative Example 14, it was not be able to fabricate asmooth cast sheet because of melt fracture at the time of extrusionmolding. For this reason, breakage occurred when the cast sheet wasstretched.

Examples 11 to 13, Comparative Example 15, and Comparative Example 16

Polypropylene films according to Examples 11 to 13, Comparative Example15, and Comparative Example 16 were obtained in the same manner as inExample 9 except that the mixing ratio at the time of dry blending ofthe raw material resins was changed as shown in Table 4.

TABLE 4 Comparative Comparative Example Example Example Example ExampleExample Example 9 10 11 12 13 9 10 Resin A1 64 64 60 60 98 65 65 (partsby mass) Resin A2 — — — — — — — (parts by mass) Resin B1 33 — — 30 — —35 (parts by mass) Resin B2 — 33 30 — — 35 — (parts by mass) Resin B3 —— — — — — — (parts by mass) Resin C1 3 3 10 10 2 — — (parts by mass)Resin X1 — — — — — — — (parts by mass) Resin X2 — — — — — — — (parts bymass) Comparative Comparative Comparative Comparative ComparativeComparative Example Example Example Example Example Example 11 12 13 1415 16 Resin A1 63 100 — — — 98 (parts by mass) Resin A2 — — 64 — — —(parts by mass) Resin B1 34 — — — — — (parts by mass) Resin B2 — — — — —— (parts by mass) Resin B3 — — 34 — — — (parts by mass) Resin C1 — — —100 2 — (parts by mass) Resin X1 3 — 2 — — 2 (parts by mass) Resin X2 —— — — 98 — (parts by mass)

<Measurement of Thickness of Polypropylene Film>

The thickness of the polypropylene films of Examples and ComparativeExamples was measured by a method similar to that described in thesection of “Examples according to first present invention”. The resultsare shown in Table 5.

<Measurement of Svk Value (Svk_(A)) of First Surface, Spk Value(Spk_(A)) of First Surface, Svk Value (Svk_(B)) of Second Surface, SpkValue (Spk_(B)) of Second Surface, Sq Value (Sq_(A)) of First Surface,Sq Value (Sq_(B)) of Second Surface, Sa Value (Sa_(A)) of First Surface,Sa Value (Sa_(B)) of Second Surface, Sk Value (Sk_(A)) of First Surface,and Sk Value (Sk_(B)) of Second Surface>

The Svk value (Svk_(A)) of the first surface, the Spk value (Spk_(A)) ofthe first surface, the Svk value (Svk_(B)) of the second surface, theSpk value (Spk_(B)) of the second surface, the Sq value (Sq_(A)) of thefirst surface, the Sq value (Sq_(B)) of the second surface, the Sa value(Sa_(A)) of the first surface, the Sa value (Sa_(B)) of the secondsurface, the Sk value (Sk_(A)) of the first surface, and the Sk value(Sk_(B)) of the second surface were determined by methods similar tothose described in the section of “Examples according to first presentinvention”. The results are shown in Table 5. Incidentally, Table 5 alsoshows the values of the ratio Spk_(B)/Spk_(A), the ratioSvk_(B)/Svk_(A), the ratio Sq_(B)/Sq_(A), the ratio Sa_(B)/Sa_(A), andthe ratio Sk_(B)/Sk_(A).

<Measurement of Ellipse Density>

The ellipse densities of the first surface (surface A) and secondsurface (surface B) of the polypropylene films of Examples andComparative Examples were measured by methods similar to those describedin the section of “Examples according to first present invention”. Theresults are shown in Table 5.

<Measurement of Average Major Axis Length>

The average value of the major axes of the ellipses observed in themeasurement of ellipse density was calculated. The results are shown inTable 5.

<Measurement of Ellipse Perfectness>

The ellipse perfectness of the polypropylene films of Examples andComparative Examples was measured by a method similar to that describedin the section of “Examples according to first present invention”. Theresults are shown in Table 5.

<Measurement of Dielectric Breakdown Strength of Polypropylene Film(Dielectric Strength Evaluation)>

The dielectric breakdown strength ES (V_(DC)/μm) of the polypropylenefilms of Examples and Comparative Examples was measured by a methodsimilar to that described in the section of “Examples according to firstpresent invention”. The results are shown in Table 5.

Incidentally, in Comparative Examples 9 and 12, it can be seen that thedielectric breakdown strength at 120° C. is less than 485 V_(DC)/μm andthe dielectric strength is poor.

<Evaluation on Blocking of Metal Vapor-Deposited Roll>

The evaluation on blocking of the metal vapor-deposited roll wasperformed by a method similar to that described in the section of“Examples according to first present invention”. The results are shownin Table 5.

<Measurement of Ash Content>

The ash content in the polypropylene film was measured by a methodsimilar to that described in the section of “Examples according to firstpresent invention”. The results are shown in Table 5.

<Evaluation on Processability in Slitting Step>

The evaluation on processability in the slitting step was performed by amethod similar to that described in the section of “Examples accordingto first present invention”. The results are shown in Table 5.

<Evaluation on Element Winding Processability>

The evaluation on element winding processability was performed by amethod similar to that described in the section of “Examples accordingto first present invention”. The results are shown in Table 5.

TABLE 5 Comparative Comparative Comparative Comparative ComparativeComparative Comparative Comparative Example Example Example ExampleExample Example Example Example Example Example Example Example Example9 10 11 12 13 9 10 11 12 13 14 15 16 Thickness [μm] 2.3 2.3 2.3 2.3 2.32.3 2.3 2.3 2.3 2.3 — 2.3 2.3 Spk [μm] Spk_(A) (Spk of 0.049 0.050 0.0400.035 0.080 0.082 0.079 0.051 0.086 0.050 — 0.073 0.041 surface A)Spk_(B) (Spk of 0.025 0.033 0.027 0.024 0.026 0.038 0.028 0.014 0.0400.014 — 0.028 0.009 surface B) Spk_(B)/Spk_(A) 0.510 0.660 0.691 0.6760.327 0.463 0.354 0.275 0.465 0.280 — 0.384 0.227 Svk [μm] Svk_(A) (Svkof 0.012 0.014 0.029 0.025 0.028 0.039 0.033 0.012 0.041 0.012 — 0.0320.029 surface A) SvK_(B) (Svk of 0.011 0.016 0.025 0.022 0.022 0.0140.009 0.009 0.014 0.010 — 0.026 0.009 surface B) Svk_(B)/Svk_(A) 0.9171.143 0.870 0.895 0.777 0.359 0.273 0.750 0.341 0.833 — 0.807 0.309 Sq[μm] Sq_(A) (Sq of 0.027 0.032 0.051 0.045 0.067 0.081 0.071 0.038 0.0890.040 — 0.066 0.050 surface A) Sq_(B) (Sq of 0.014 0.022 0.042 0.0370.038 0.028 0.017 0.010 0.031 0.011 — 0.043 0.015 surface B)Sq_(B)/Sq_(A) 0.519 0.688 0.827 0.827 0.563 0.346 0.239 0.263 0.3480.275 — 0.659 0.297 Sa [μm] Sa_(A) (Sa of 0.014 0.017 0.017 0.015 0.0200.019 0.016 0.014 0.020 0.014 — 0.020 0.017 surface A) Sa_(B) (Sa of0.010 0.014 0.014 0.013 0.013 0.011 0.008 0.008 0.012 0.09 — 0.015 0.005surface B) Sa_(B)/Sa_(A) 0.714 0.824 0.840 0.834 0.655 0.579 0.500 0.5710.600 0.600 — 0.726 0.306 Sk [μm] Sk_(A) (Sk of 0.038 0.043 0.050 0.0460.052 0.043 0.038 0.040 0.045 0.039 — 0.056 0.048 surface A) Sk_(B) (Skof 0.031 0.037 0.043 0.038 0.039 0.031 0.024 0.023 0.032 0.024 — 0.0440.015 surface B) Sk_(B)/Sk_(A) 0.816 0.860 0.855 0.839 0.738 0.721 0.6320.575 0.711 0.615 — 0.790 0.316 Ellipse D_(A) (ellipse 93 85 119 117 8674 81 80 75 81 — 83 80 density density on [pieces/mm²] surface A) D_(B)(ellipse 6 11 7 6 12 14 6 0 13 0 — 11 0 density on surface B)D_(B)/D_(A) 0.0645 0.1294 0.0588 0.0513 0.1395 0.1892 0.0741 0.00000.1733 0.0000 — 0.1325 0.0000 Average L_(A) (average 51 56 39 41 89 8980 70 90 70 — 52 73 major axis major axis length [μm] length on surfaceA) L_(B) (average 57 53 43 47 110 111 118 — 110 — — 60 — major axislength on surface B) L_(B)/L_(A) 1.118 0.946 1.103 1.146 1.236 1.2471.475 — 1.222 — — 1.154 — Ellipse P_(A) (ellipse 44 50 60 63 50 51 45 3951 40 — 44 43 perfectness perfectness [%] on surface A) P_(B) (ellipse28 32 37 41 31 35 30 13 36 14 — 29 — perfectness on surface B)P_(B)/P_(A) 0.636 0.640 0.617 0.651 0.620 0.686 0.667 0.333 0.706 0.350— 0.659 — Dielectric [V_(DC)/μm] 543 530 555 561 534 528 542 532 504 530— 531 520 breakdown strength at 100° C. Dielectric [V_(DC)/μm] 515 500505 506 490 482 505 486 462 485 — 480 475 breakdown strength at 120° C.Ash content [ppm] 3 × 10 3 × 10 5 × 10 5 × 10 3 × 10 2 × 10 2 × 10 4 ×10 2 × 10 3 × 10 35 × 10 2 × 10 3 × 10 Evaluation on blocking AA AA AAAA AA A C C A C — A C suppressing property of metal vapor-deposited rollEvaluation on processability A A A A A C D C C C — C C in slitting stepEvaluation on element ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ — ○ ○ winding processability

<Fabrication of Capacitor and Capacitance>

Capacitors were fabricated as follows using the polypropylene filmsobtained in Examples. A metal layer-integrated polypropylene filmincluding a metal film on either surface of the polypropylene film wasobtained by subjecting the polypropylene film to aluminum vapordeposition at a vapor deposition resistance of 15Ω/□ to form a T-marginvapor deposition pattern. After the film was slit into a width of 60 mm,two metal layer-integrated polypropylene films were combined and woundby 1076 turns at a winding tension of 250 g using an automated winder3KAW-N2 available from KAIDO MFG. CO., LTD. The wound element wassubjected to a heat treatment at 120° C. for 15 hours under pressing,and then zinc metal was thermally sprayed on the element end surface toobtain a flat-shaped capacitor. A lead wire was soldered to the endsurface of the flat-shaped capacitor, and the flat-shaped capacitor wasthen sealed with epoxy resin. The capacitances of the finishedcapacitors were all 75 μF (±5 μF).

Heretofore, Examples according to the second present invention has beendescribed.

Examples According to Third Present Invention

Next, Examples according to the third present invention will bedescribed.

Polypropylene films of the following Examples and Comparative Exampleswere fabricated using the polypropylene resins (Resin A1, Resin A2,Resin B1, Resin B2, Resin C1, Resin X1, and Resin X2) described in thesection of “Examples according to first present invention”, and thephysical properties thereof were evaluated.

Fabrication of Polypropylene Film Example 14

Resin A1, Resin B1, and Resin C1 were dry-blended. The mixing ratio wasset to (Resin A1):(Resin B1):(Resin C1)=63:34:3 in terms of mass ratio.After that, the dry-blended resin was melted at a resin temperature of250° C., then extruded using a T die, wound around a metal drum of whichthe surface temperature was kept at 95° C., and solidified to fabricatea cast sheet. At this time, the cast sheet was fabricated while pressingthe melt-extruded resin composition against the metal drum with an airknife. The unstretched cast sheet obtained was kept at a temperature of130° C., and allowed to pass between rolls running at different speedsto be stretched to 4.5 times in the machine direction, and immediatelycooled to room temperature. Subsequently, the stretched sheet was guidedto the tenter, and stretched to 8 times in the width direction at atemperature of 158° C., and then subjected to relaxation andthermosetting, and wound, and subjected to an aging treatment in anatmosphere at about 40° C. to obtain a polypropylene film according toExample 14.

Example 15 and Comparative Examples 17 to 22

Polypropylene films according to Example 15 and Comparative Examples 17to 22 were obtained in the same manner as in Example 14 except that themixing ratio at the time of dry blending of the raw material resins waschanged as shown in Table 6.

However, in Comparative Example 22, it was not be able to fabricate asmooth cast sheet because of melt fracture at the time of extrusionmolding. For this reason, breakage occurred when the cast sheet wasstretched.

Examples 16 to 18, Comparative Example 23, and Comparative Example 24

Polypropylene films according to Examples Examples 16 to 18, ComparativeExample 23, and Comparative Example 24 were obtained in the same manneras in Example 14 except that the mixing ratio at the time of dryblending of the raw material resins was changed as shown in Table 6.

TABLE 6 Example Example Example Example Example Example ExampleComparative Comparative 14 15 16 17 18 17 18 Resin A1 63 62 60 60 98 6565 (parts by mass) Resin A2 — — — — — — — (parts by mass) Resin B1 34 —— 30 — — 35 (parts by mass) Resin B2 — 35 30 — — 35 — (parts by mass)Resin B3 — — — — — — — (parts by mass) Resin C1 3 3 10 10 2 — — (partsby mass) Resin X1 — — — — — — — (parts by mass) Resin X2 — — — — — — —(parts by mass) Example Example Comparative Comparative ComparativeComparative Comparative Comparative Example Example Example Example 1920 21 22 23 24 Resin A1 63 100 — — — 98 (parts by mass) Resin A2 — — 64— — — (parts by mass) Resin B1 34 — — — — — (parts by mass) Resin B2 — —— — — — (parts by mass) Resin B3 — — 34 — — — (parts by mass) Resin C1 —— — 100 2 — (parts by mass) Resin X1 3 — 2 — — 2 (parts by mass) ResinX2 — — — — 98 — (parts by mass)

<Measurement of Thickness of Polypropylene Film>

The thickness of the polypropylene films of Examples and ComparativeExamples was measured by a method similar to that described in thesection of “Examples according to first present invention”. The resultsare shown in Table 7.

<Measurement of Ellipse Density>

The ellipse densities of the first surface (surface A) and secondsurface (surface B) of the polypropylene films of Examples andComparative Examples were measured by methods similar to those describedin the section of “Examples according to first present invention”. Theresults are shown in Table 7.

<Measurement of Average Major Axis Length>

The average value of the major axes of the ellipses observed in themeasurement of ellipse density was calculated. The results are shown inTable 7.

<Measurement of Ellipse Perfectness>

The ellipse perfectness of the polypropylene films of Examples andComparative Examples was measured by a method similar to that describedin the section of “Examples according to first present invention”. Theresults are shown in Table 7.

<Measurement of Sq Value (Sq_(A)) of First Surface, Sq Value (Sq_(B)) ofSecond Surface, Sa Value (Sa_(A)) of First Surface, Sa Value (Sa_(B)) ofSecond Surface, Sk Value (Sk_(A)) of First Surface, and Sk Value(Sk_(B)) of Second Surface>

The Sq value (Sq_(A)) of the first surface, the Sq value (Sq_(B)) of thesecond surface, the Sa value (Sa_(A)) of the first surface, the Sa value(Sa_(B)) of the second surface, the Sk value (Sk_(A)) of the firstsurface, and the Sk value (Sk_(B)) of the second surface were determinedby methods similar to those described in the section of “Examplesaccording to first present invention”. The results are shown in Table 7.Incidentally, Table 7 also shows the values of the ratio Sq_(B)/Sq_(A),the ratio Sa_(B)/Sa_(A), and the ratio Sk_(B)/Sk_(A).

<Measurement of Dielectric Breakdown Strength of Polypropylene Film(Dielectric Strength Evaluation)>

The dielectric breakdown strength ES (Vcc/μm) of the polypropylene filmsof Examples and Comparative Examples was measured by a method similar tothat described in the section of “Examples according to first presentinvention”. The results are shown in Table 7.

Incidentally, in Comparative Examples 17 and 20, it can be seen that thedielectric breakdown strength at 120° C. is less than 485 Vcc/μm and thedielectric strength is poor.

<Evaluation on Blocking of Metal Vapor-Deposited Roll>

The evaluation on blocking of the metal vapor-deposited roll wasperformed by a method similar to that described in the section of“Examples according to first present invention”. The results are shownin Table 7.

<Measurement of Ash Content>

The ash content in the polypropylene film was measured by a methodsimilar to that described in the section of “Examples according to firstpresent invention”. The results are shown in Table 7.

<Evaluation on Processability in Slitting Step>

The evaluation on processability in the slitting step was performed by amethod similar to that described in the section of “Examples accordingto first present invention”. The results are shown in Table 7.

<Evaluation on Element Winding Processability>

The evaluation on element winding processability was performed by amethod similar to that described in the section of “Examples accordingto first present invention”. The results are shown in Table 7.

TABLE 7 Comparative Comparative Comparative Comparative ComparativeComparative Comparative Comparative Example Example Example ExampleExample Example Example Example Example Example Example Example Example14 15 16 17 18 17 18 19 20 21 22 23 24 Thickness [μm] 2.3 2.3 2.3 2.32.3 2.3 2.3 2.3 2.3 2.3 — 2.3 2.3 Ellipse D_(A) (ellipse 94 87 119 11786 74 81 80 75 81 — 83 80 density density on [pieces/mm²] surface A)D_(B) (ellipse 6 11 7 6 12 14 6 0 13 0 — 11 0 density on surface B)D_(B)/D_(A) 0.0638 0.1264 0.0588 0.0513 0.1395 0.1892 0.0741 0.00000.1733 0.0000 — 0.1325 0.0000 Average L_(A) (average 51 56 39 41 89 8980 70 90 70 — 52 73 major axis major axis length [μm] length on surfaceA) L_(B) (average 57 55 43 47 110 111 118 — 110 — — 60 — major axisength on surface B) L_(B)/L_(A) 1.118 0.982 1.103 1.146 1.236 1.2471.475 — 1.222 — — 1.154 — Ellipse P_(A) (ellipse 43 48 60 63 50 51 45 3951 40 — 44 43 perfectness perfectness on [%] surface A) P_(B) (ellipse27 32 37 41 31 35 30 13 36 14 — 29 — perfectness on surface B)P_(B)/P_(A) 0.628 0.667 0.617 0.651 0.620 0.686 0.667 0.333 0.706 0.350— 0.659 — Sq [μm] Sq_(A) (Sq of 0.028 0.032 0.051 0.045 0.067 0.0810.071 0.038 0.089 0.040 — 0.066 0.050 surface A) Sq_(B) (Sq of 0.0140.022 0.042 0.037 0.038 0.028 0.017 0.010 0.031 0.011 — 0.043 0.015surface B) Sq_(B)/Sq_(A) 0.500 0.688 0.827 0.827 0.563 0.346 0.239 0.2630.348 0.275 — 0.659 0.297 Sa [μm] Sa_(A) (Sa of 0.014 0.018 0.017 0.0150.020 0.019 0.016 0.014 0.020 0.014 — 0.020 0.017 surface A) Sa_(B) (Saof 0.010 0.013 0.014 0.013 0.013 0.011 0.008 0.008 0.012 0.09 — 0.0150.005 surface B) Sa_(B)/Sa_(A) 0.714 0.722 0.840 0.834 0.655 0.579 0.5000.571 0.600 0.600 — 0.726 0.306 Sk [μm] Sk_(A) (Sk of 0.040 0.043 0.0500.046 0.052 0.043 0.038 0.040 0.045 0.039 — 0.056 0.048 surface A)Sk_(B) (Sk of 0.031 0.037 0.043 0.038 0.039 0.031 0.024 0.023 0.0320.024 — 0.044 0.015 surface B) Sk_(B)/Sk_(A) 0.775 0.860 0.855 0.8390.738 0.721 0.632 0.575 0.711 0.615 — 0.790 0.316 Dielectric [V_(DC)/μm]543 530 555 561 534 528 542 532 504 530 — 531 520 breakdown strength at100° C. Dielectric [V_(DC)/μm] 515 500 505 506 490 482 505 486 462 485 —480 475 breakdown strength at 120° C. Ash content [ppm] 3 × 10 3 × 10 5× 10 5 × 10 3 × 10 2 × 10 2 × 10 4 × 10 2 × 10 3 × 10 35 × 10 2 × 10 3 ×10 Evaluation on blocking AA AA AA AA AA A C C A C — A C suppressingproperty of metal vapor-deposited roll Evaluation on processability A AA A A C D C C C — C C in slitting step Evaluation on element ○ ○ ○ ○ ○ ○○ ○ ○ ○ — ○ ○ winding processability

<Fabrication of Capacitor and Capacitance>

Capacitors were fabricated as follows using the polypropylene filmsobtained in Examples. A metal layer-integrated polypropylene filmincluding a metal film on either surface of the polypropylene film wasobtained by subjecting the polypropylene film to aluminum vapordeposition at a vapor deposition resistance of 15Ω/□ to form a T-marginvapor deposition pattern. After the film was slit into a width of 60 mm,two metal layer-integrated polypropylene films were combined and woundby 1076 turns at a winding tension of 250 g using an automated winder3KAW-N2 available from KAIDO MFG. CO., LTD. The wound element wassubjected to a heat treatment at 120° C. for 15 hours under pressing,and then zinc metal was thermally sprayed on the element end surface toobtain a flat-shaped capacitor. A lead wire was soldered to the endsurface of the flat-shaped capacitor, and the flat-shaped capacitor wasthen sealed with epoxy resin. The capacitances of the finishedcapacitors were all 75 μF (±5 μF).

Heretofore, Examples according to the third present invention has beendescribed.

What is claimed is:
 1. A polypropylene film having a first surface and asecond surface, wherein: the polypropylene film contains a polypropyleneresin as a main component; an ellipse density D_(A) on the first surfaceis 85 to 120 pieces/mm²; and an ellipse density D_(B) on the secondsurface is 1 to 12 pieces/mm².
 2. The polypropylene film according toclaim 1, wherein the polypropylene film is biaxially stretched.
 3. Thepolypropylene film according to claim 1, wherein an average major axislength LA of the ellipses constituting the ellipse density D_(A) on thefirst surface is 20 to 80 μm, and an average major axis length L_(B) ofthe ellipses constituting the ellipse density D_(B) on the secondsurface is 30 to 100 μm.
 4. The polypropylene film according to claim 1,wherein the polypropylene resin contains: a linear polypropylene resin Ahaving a difference of 8.0% or more attained by subtracting adifferential distribution value when a logarithmic molecular weight Log(M)=6.0 from a differential distribution value when a logarithmicmolecular weight Log (M)=4.5 in a molecular weight differentialdistribution curve; a linear polypropylene resin B having a differenceof less than 8.0% attained by subtracting a differential distributionvalue when a logarithmic molecular weight Log (M)=6.0 from adifferential distribution value when a logarithmic molecular weight Log(M)=4.5 in a molecular weight differential distribution curve; and along-chain branched polypropylene resin C polymerized using ametallocene catalyst.
 5. A metal layer-integrated polypropylene filmcomprising: the polypropylene film according to claim 1; and a metallayer stacked on either surface or both surfaces of the polypropylenefilm.
 6. A film capacitor comprising the metal layer-integratedpolypropylene film according to claim 5 that is wound, or in aconfiguration in which a plurality of the metal layer-integratedpolypropylene films are stacked.
 7. A film roll comprising thepolypropylene film according to claim 1 that is wound into a roll.